| 1. | Paget's Disease, Mammary (2 recruiting studies) |
| 2. | Pain (90 recruiting studies) |
| 3. | Pallister-Hall Syndrome (1 recruiting study) |
| 4. | Pancreatic Diseases (72 recruiting studies) |
| 5. | Pancreatic Insufficiency (1 recruiting study) |
| 6. | Pancreatic Neoplasms (54 recruiting studies) |
| 7. | Pancreatitis (3 recruiting studies) |
| 8. | Pancreatitis, Acute Necrotizing (2 recruiting studies) |
| 9. | Pancytopenia (7 recruiting studies) |
| 10. | Panic Disorder (9 recruiting studies) |
| 11. | Panuveitis (2 recruiting studies) |
| 12. | Papilledema (3 recruiting studies) |
| 13. | Papilloma (13 recruiting studies) |
| 14. | Papillomavirus Infections (1 recruiting study) |
| 15. | Paraganglioma (2 recruiting studies) |
| 16. | Paragonimiasis (1 recruiting study) |
| 17. | Paralysis (19 recruiting studies) |
| 18. | Paranasal Sinus Diseases (5 recruiting studies) |
| 19. | Paranasal Sinus Neoplasms (5 recruiting studies) |
| 20. | Paraneoplastic Syndromes (5 recruiting studies) |
| 21. | Paranoid Behavior (1 recruiting study) |
| 22. | Paranoid Disorders (3 recruiting studies) |
| 23. | Paraparesis (3 recruiting studies) |
| 24. | Paraparesis, Spastic (3 recruiting studies) |
| 25. | Paraparesis, Tropical Spastic (2 recruiting studies) |
| 26. | Paraplegia (3 recruiting studies) |
| 27. | Paraproteinemias (58 recruiting studies) |
| 28. | Parapsoriasis (1 recruiting study) |
| 29. | Parasitic Diseases (18 recruiting studies) |
| 30. | Parasitic Diseases, Animal (3 recruiting studies) |
| 31. | Parasomnias (2 recruiting studies) |
| 32. | Parathyroid Diseases (6 recruiting studies) |
| 33. | Parathyroid Neoplasms (3 recruiting studies) |
| 34. | Paresis (2 recruiting studies) |
| 35. | Paresthesia (1 recruiting study) |
| 36. | Parkes-Weber Syndrome (16 recruiting studies) |
| 37. | Parkinson Disease (37 recruiting studies) |
| 38. | Parkinsonian Disorders (34 recruiting studies) |
| 39. | Pathologic Processes (177 recruiting studies) |
| 40. | Pathological Conditions, Anatomical (6 recruiting studies) |
| 41. | Pathological Conditions, Signs and Symptoms (387 recruiting studies) |
| 42. | Pelvic Neoplasms (1 recruiting study) |
| 43. | Pelvic Pain (4 recruiting studies) |
| 44. | Pemphigus (1 recruiting study) |
| 45. | Penile Diseases (2 recruiting studies) |
| 46. | Penile Neoplasms (2 recruiting studies) |
| 47. | Pentalogy of Cantrell (1 recruiting study) |
| 48. | Peptic Ulcer (7 recruiting studies) |
| 49. | Peptic Ulcer Hemorrhage (2 recruiting studies) |
| 50. | Perceptual Disorders (4 recruiting studies) |
| 51. | Periodontal Diseases (7 recruiting studies) |
| 52. | Periodontitis (3 recruiting studies) |
| 53. | Peripheral Nervous System Diseases (23 recruiting studies) |
| 54. | Peripheral Nervous System Neoplasms (9 recruiting studies) |
| 55. | Peripheral Vascular Diseases (8 recruiting studies) |
| 56. | Peritoneal Diseases (6 recruiting studies) |
| 57. | Peritoneal Neoplasms (5 recruiting studies) |
| 58. | Peritonitis (1 recruiting study) |
| 59. | Peroxisomal Disorders (3 recruiting studies) |
| 60. | Persian Gulf Syndrome (1 recruiting study) |
| 61. | Personality Disorders (4 recruiting studies) |
| 62. | Peutz-Jeghers Syndrome (1 recruiting study) |
| 63. | Phagocyte Bactericidal Dysfunction (10 recruiting studies) |
| 64. | Pharyngeal Diseases (32 recruiting studies) |
| 65. | Pharyngeal Neoplasms (32 recruiting studies) |
| 66. | Pheochromocytoma (4 recruiting studies) |
| 67. | Philadelphia Chromosome (29 recruiting studies) |
| 68. | Phlebitis (3 recruiting studies) |
| 69. | Phobic Disorders (5 recruiting studies) |
| 70. | Photosensitivity Disorders (2 recruiting studies) |
| 71. | Phyllodes Tumor (1 recruiting study) |
| 72. | Pick Disease of the Brain (4 recruiting studies) |
| 73. | Picornaviridae Infections (4 recruiting studies) |
| 74. | Pigmentation Disorders (5 recruiting studies) |
| 75. | Pituitary Diseases (11 recruiting studies) |
| 76. | Pituitary Neoplasms (6 recruiting studies) |
| 77. | Placenta Diseases (2 recruiting studies) |
| 78. | Plant Poisoning (1 recruiting study) |
| 79. | Plasmacytoma (93 recruiting studies) |
| 80. | Platelet Storage Pool Deficiency (3 recruiting studies) |
| 81. | Pleural Diseases (4 recruiting studies) |
| 82. | Pleural Effusion (3 recruiting studies) |
| 83. | Pleural Effusion, Malignant (2 recruiting studies) |
| 84. | Pleural Neoplasms (3 recruiting studies) |
| 85. | Pneumocystis Infections (1 recruiting study) |
| 86. | Pneumonia (21 recruiting studies) |
| 87. | Pneumonia, Aspiration (1 recruiting study) |
| 88. | Pneumonia, Bacterial (1 recruiting study) |
| 89. | Pneumonia, Pneumocystis (1 recruiting study) |
| 90. | Pneumothorax (2 recruiting studies) |
| 91. | Poisoning (28 recruiting studies) |
| 92. | Poliomyelitis (3 recruiting studies) |
| 93. | Polycystic Kidney Diseases (2 recruiting studies) |
| 94. | Polycystic Kidney, Autosomal Dominant (1 recruiting study) |
| 95. | Polycystic Kidney, Autosomal Recessive (1 recruiting study) |
| 96. | Polycystic Ovary Syndrome (1 recruiting study) |
| 97. | Polycythemia (16 recruiting studies) |
| 98. | Polycythemia Vera (16 recruiting studies) |
| 99. | Polydactyly (2 recruiting studies) |
| 100. | Polymyositis (7 recruiting studies) |
| 101. | Polyneuropathies (3 recruiting studies) |
| 102. | Polyps (2 recruiting studies) |
| 103. | Polyradiculoneuropathy (2 recruiting studies) |
| 104. | Polyradiculopathy (1 recruiting study) |
| 105. | Porencephaly (1 recruiting study) |
| 106. | Porphyria (1 recruiting study) |
| 107. | Porphyria, Erythropoietic (1 recruiting study) |
| 108. | Postoperative Complications (15 recruiting studies) |
| 109. | Postoperative Nausea and Vomiting (2 recruiting studies) |
| 110. | Postpoliomyelitis Syndrome (3 recruiting studies) |
| 111. | Pouchitis (1 recruiting study) |
| 112. | Poxviridae Infections (3 recruiting studies) |
| 113. | Prader-Willi Syndrome (1 recruiting study) |
| 114. | Precancerous Conditions (6 recruiting studies) |
| 115. | Prediabetic State (1 recruiting study) |
| 116. | Pregnancy Complications (310 recruiting studies) |
| 117. | Pregnancy Complications, Infectious (2 recruiting studies) |
| 118. | Pregnancy Complications, Neoplastic (1 recruiting study) |
| 119. | Preleukemia (172 recruiting studies) |
| 120. | Premenstrual Syndrome (4 recruiting studies) |
| 121. | Prolapse (1 recruiting study) |
| 122. | Prostatic Diseases (155 recruiting studies) |
| 123. | Prostatic Hyperplasia (5 recruiting studies) |
| 124. | Prostatic Neoplasms (150 recruiting studies) |
| 125. | Protein Deficiency (1 recruiting study) |
| 126. | Protein-Energy Malnutrition (1 recruiting study) |
| 127. | Proteinuria (5 recruiting studies) |
| 128. | Proteus Syndrome (1 recruiting study) |
| 129. | Protozoan Infections (11 recruiting studies) |
| 130. | Protozoan Infections, Animal (3 recruiting studies) |
| 131. | Pruritus (1 recruiting study) |
| 132. | Pseudohypoparathyroidism (1 recruiting study) |
| 133. | Pseudomonas Infections (1 recruiting study) |
| 134. | Pseudopseudohypoparathyroidism (1 recruiting study) |
| 135. | Pseudotumor Cerebri (1 recruiting study) |
| 136. | Psoriasis (8 recruiting studies) |
| 137. | Psychological Phenomena and Processes (25 recruiting studies) |
| 138. | Psychomotor Agitation (8 recruiting studies) |
| 139. | Psychomotor Disorders (2 recruiting studies) |
| 140. | Psychophysiology (28 recruiting studies) |
| 141. | Psychotic Disorders (95 recruiting studies) |
| 142. | Puberty, Precocious (2 recruiting studies) |
| 143. | Puerperal Disorders (6 recruiting studies) |
| 144. | Pulmonary Alveolar Proteinosis (1 recruiting study) |
| 145. | Pulmonary Disease, Chronic Obstructive (4 recruiting studies) |
| 146. | Pulmonary Edema (1 recruiting study) |
| 147. | Pulmonary Embolism (3 recruiting studies) |
| 148. | Pulmonary Emphysema (2 recruiting studies) |
| 149. | Pulmonary Fibrosis (8 recruiting studies) |
| 150. | Pulmonary Heart Disease (1 recruiting study) |
| 151. | Purine-Pyrimidine Metabolism, Inborn Errors (1 recruiting study) |
| 152. | Purpura (3 recruiting studies) |
| 153. | Purpura, Thrombocytopenic (3 recruiting studies) |
