| Abbreviations | Meaning |
 | OPDS | Otopalatodigital Syndrome |
 | OPS | Operations; Optical Position Sensor; Osteoporosis-pseudolipoma Syndrome; Outpatient Service; Outpatient Surgery |
 | OPS | Operations; Optical Position Sensor; Optimal Parameter Search [algorithm]; Osteoporosis-pseudolipoma Syndrome; Outpatient Service; Outpatient Surgery |
 | OPUS | Orbofiban In Patients With Unstable Coronary Syndromes [study] |
 | ORC | Oculo-reno-cerebellar [syndrome] |
 | ORC | Oculo-reno-cerebellar [syndrome]; Origin Recognition Complex |
 | ORS | Olfactory Reference Syndrome |
 | ORW | Osler-Rendu-Weber (syndrome) |
 | ORW | Osler-Rendu-Weber [syndrome] |
 | OS | Omenn Syndrome |
 | OS | Opitz Syndrome |
 | OS-CS | Osteopathia Striata-cranial Sclerosis [syndrome] |
 | OSAS | Obstructive Sleep Apnea Syndrome |
 | OU | Observation Unit; Oppenheimer-Urbach [syndrome] |
 | OUS | Overuse Syndrome |
 | OWR | Osler-Weber-Rendu [syndrome]; Ovarian Wedge Resection |
 | OWS | Outerwear Syndrome |
 | PAC | Pericarditis-arthropathy-camptodactyly [syndrome] |
 | PACT | Prospective Acute Coronary Syndrome Trial |
 | PAGOD | Pulmonary Hypoplasia-hypoplasia Of Pulmonary Artery-agonadism-omphalocele/diaphragmatic Defect-dextrocardia [syndrome] |
 | PAIDS | Paralyzed Academic Investigator's Disease Syndrome; Pediatric Acquired Immunodeficiency Syndrome |
 | PAIS | Partial Androgen Insensitivity Syndrome |
 | PAIS | Pravastatin In Acute Ischemic Syndromes [study] |
 | PALS | Prison-acquired Lymphoproliferative Syndrome |
 | PANSS | Positive And Negative Syndrome Scale |
 | PAPS | 3´-phosphoadenosine-5´-phosphosulfate; Primary Antiphospholipid Antibody Syndrome |
 | PARAGON | Platelet IIb/IIIa Antagonist For The Reduction Of Acute Coronary Syndrome Events In A Global Organization Network [study] |
 | PAWS | Primary Withdrawal Syndrome |
 | PBS | Perfusion-pressure Breakthrough Syndrome |
 | PBS | Prune Belly Syndrome |
 | PCIS | Patient-Care Information System; Point-of-care Information System; Postcardiac Injury Syndrome |
 | PCOS | Polycystic Ovary Syndrome |
 | PCS | Pelvic Congestion Syndrome |
 | PCS | Pharmacogenic Confusional Syndrome |
 | PCS | Postcardiotomy Syndrome |
 | PCS | Postcholecystectomy Syndrome |
 | PCS | Postconcussion Syndrome |
 | PCS | Prolonged Crush Syndrome |
 | PD/AR | Photosensitivity Dermatitis And Actinic Reticuloid Syndrome |
 | PDGS | Partial Form Of DiGeorge Syndrome |
 | PDS | Pain-dysfunction Syndrome |
 | PDSG | Pigment Dispersion Syndrome Glaucoma |
 | PEAS | Patient Education And Activation System; Possible Estuary-associated Syndrome |
 | PEHO | Progressive Encephalopathy-edema-hypsarrhythmia-optic Atrophy [syndrome] |
 | PEP | Pigmentation, Edema, And Plasma Cell Dyscrasia [syndrome] |
 | PES | Physical Examination Syndrome |
 | PES | Preexcitation Syndrome |
 | PES | Primary Empty Sella [syndrome] |
 | PES | Pseudoexfoliation Or Pseudoexfoliative Syndrome |
 | PFPS | Patellofemoral Pain Syndrome |