See Rare Diseases by First Letter (P)
- Pachyonychia Congenita
- Paget Disease, Extramammary
- Palatopharyngeal Incompetence
- Pallister-Hall Syndrome
- Palmoplantar Keratoderma
- Pancreatic Adenoma
- Pancreatic Cancer
- Pancreatic Carcinoma, Familial
- Pancreatic Islet Cell Tumors
- PANDAS
- Pantothenate Kinase-associated Neurodegeneration
- Panuveitis
- Papillary Renal Cell Carcinoma
- Papilledema
- Papillon Lefevre Syndrome
- Paragangliomas 1
- Parainfluenza Virus Type 3
- Paramyotonia Congenita
- Paraplegia
- Parapsoriasis
- Parathyroid Carcinoma
- Parkes Weber Syndrome
- Paroxysmal Nocturnal Hemoglobinuria
- Paroxysmal Ventricular Fibrillation
- Pars Planitis
- Patent Ductus Arteriosus
- Pearson Syndrome
- Pectus Carinatum
- Pediatric Crohns Disease
- Pediatric Multiple Sclerosis
- Pediatric Ulcerative Colitis
- Pelizaeus-Merzbacher Disease
- Pemphigus
- Pemphigus Vulgaris
- Penis Agenesis
- Pentalogy of Cantrell
- Periarteritis Nodosa
- Periodic Fever, Familial, Autosomal Dominant
- Peripartum Cardiomyopathy
- Peripheral T-cell Lymphoma
- Periventricular Leukomalacia
- Peroxisome Biogenesis Disorders
- Persistent Truncus Arteriosus
- Peutz Jeghers Syndrome
- Peyronie Disease
- Pfeiffer Syndrome
- PHACE Syndrome
- Phenylketonuria
- Pheochromocytoma
- Phosphoglycerate Kinase Deficiency
- Photosensitive Epilepsy
- Pick's Disease
- Piebaldism
- Pierre Robin Sequence
- Pigment-dispersion Syndrome
- Pigmentary Retinopathy
- Pigmented Villonodular Synovitis
- Pilocytic Astrocytoma
- Pilomatrixoma
- Pineoblastoma
- Pineoblastoma, Childhood
- Pineocytoma
- Piriformis Syndrome
- Pityriasis Rubra Pilaris
- Plagiocephaly
- Plasma Cell Leukemia
- Plasma Thromboplastin Antecedent Deficiency
- Platelet Storage Pool Deficiency
- Pleomorphic Malignant Fibrous Histiocytoma
- Pleomorphic Xanthoastrocytoma
- Pleuropulmonary Blastoma
- Pneumocystosis
- Pneumonia, Eosinophilic
- POEMS Syndrome
- Poliomyelitis
- Polyarteritis Nodosa
- Polyarticular Onset Juvenile Idiopathic Arthritis
- Polycystic Liver Disease
- Polycythemia Vera
- Polydactyly
- Polyembryoma
- Polymorphic Catecholergic Ventricular Tachycardia
- Polymyositis
- Polyomavirus Allograft Nephropathy
- Porencephaly
- Porokeratosis of Mibelli
- Porphyria
- Porphyria Cutanea Tarda
- Post Polio Syndrome
- Post-transplant Lymphoproliferative Disease
- Post-traumatic Epilepsy
- Posterior Urethral Valves
- Posterior Uveitis
- Postural Orthostatic Tachycardia Syndrome
- Prader-Willi Syndrome
- Precocious Puberty
- Premature Ovarian Failure, Familial
- Priapism
- Primary Agammaglobulinemia
- Primary Biliary Cirrhosis
- Primary Carnitine Deficiency
- Primary Ciliary Dyskinesia
- Primary Effusion Lymphoma
- Primary Hyperoxaluria Type 1
- Primary Lateral Sclerosis
- Primary Pigmented Nodular Adrenocortical Disease
- Primary Progressive Aphasia
- Primary Sclerosing Cholangitis
- Prinzmetal's Variant Angina
- Progeria
- Progressive Hemifacial Atrophy
- Progressive Multifocal Leukoencephalopathy
- Progressive Myoclonic Epilepsy
- Progressive Non-fluent Aphasia
- Progressive Supranuclear Palsy
- Prolactinoma, Familial
- Propionic Acidemia
- Proteus Syndrome
- Protoporphyria
- Prurigo Nodularis
- Pseudo-Turner Syndrome
- Pseudocholinesterase Deficiency
- Pseudohypoparathyroidism
- Pseudohypoparathyroidism Type 1A
- Pseudomyotonia
- Pseudomyxoma Peritonei
- Pseudopelade of Brocq
- Pseudopseudohypoparathyroidism
- Pseudotumor Cerebri
- Pseudoxanthoma Elasticum
- Pterygium of the Conjunctiva and Cornea
- Pudendal Neuralgia
- Pulmonary Arteriovenous Malformation
- Pulmonary Edema of Mountaineers
- Pulmonary Surfactant Protein B, Deficiency of
- Pulmonary Valve Stenosis
- Pulmonary Vein Stenosis
- Pulmonary Venoocclusive Disease
- Pulmonary Venous Return Anomaly
- Pulmonic Stenosis
- Punctate Inner Choroidopathy
- Pure Autonomic Failure
- Pure Red Cell Aplasia
- Pyoderma Gangrenosum
- Pyridoxine Deficiency
- Pyropoikilocytosis Hereditary