| Abbreviations | Meaning |
 | NMTCB | Nuclear Medicine Technology Certification Board |
 | NNEB | National Nursery Examination Board |
 | NOA | National Optometric Association; Nitro-L-arginine |
 | NOTB | National Ophthalmic Treatment Board |
 | NOV | Nederlandse Orthopaedisch Vereniging (Dutch Orthopaedic Association) |
 | NPA | National Pharmaceutical Association |
 | NRHA | National Rural Health Association |
 | NRPB | National Radiological Protection Board |
 | NSA | National Stroke Association |
 | NSA | Neurological Society Of America |
 | NSCC | National Society For Crippled Children |
 | NSCIA | National Spinal Cord Injury Association |
 | NSCT | National Society Of Cardiovascular Technologists |
 | NSGC | National Society Of Genetic Counselors |
 | NSH | National Society For Histotechnology |
 | NSMR | National Society For Medical Research |
 | NSNA | National Student Nurse Association |
 | NSPB | National Society For The Prevention Of Blindness |
 | NWDA | National Wholesale Druggists' Association |
 | NWDA | National Wholesale Druggists Association |
 | NWOTA | North West Orthopaedic Trainees Association |
 | NYHA | New York Heart Association |
 | NYHAFC | New York Heart Association Functional Class |
 | OAA | Old Age Assistance; Older Americans Act; Opticians Association Of America; Oxaloacetic Acid |
 | OARS | Osteoarthritis Research Society |
 | OATA | Ohio Athletic Trainers Association |
 | OLSNA | Orthopaedic Laser Society Of North America |
 | OMRT | Ontario Association Of Medical Radiation Technologists |
 | ONS | Oncology Nursing Society |
 | OOSS | Outpatient Ophthalmic Surgery Society |
 | ORA | Orthopaedic Rehabilitation Association (AAOS Specialty Societies) |
 | ORS | Orthopaedic Research Society (also: AAOS Specialty Societies) |
 | ORS | Orthopaedic Research Society |
 | ORS-ROC | Orthopedic Research Society, Republic Of China |
 | OSA | Optical Society Of America |
 | OSMT | Ontario Society Of Medical Technologists |
 | OSTOP | Osteoporosis Society Of British Columbia |
 | OSUK | Ophthalmological Society Of The United Kingdom |
 | OTA | Orthopaedic Trauma Association (Newsletter) (also: AAOS Specialty Societies) |
 | PACT | Philadelphia Association Of Clinical Trials |
 | PAFAMS | Pan-American Federation Of Associations Of Medical Schools |
 | PASSOR | Physiatric Association For Spine, Sports, And Occupational Rehabilitation |
 | PCB | Paracervical Block; Polychlorinated Biphenyl; Portacaval Bypass; Postcoital Bleeding; Printed Circuit Board; Procarbazine |
 | PCBA | Printed Circuit Board Assembled |
 | PDRB | Permanent Disbility Rating Board |
 | PDS | Patient-Doctor Society |
 | PERT | Phenol-enhanced Reassociation Technique; Program Evaluation Review Technique |
 | PFOLA | Prescription Foot Orthotic Laboratory Association |
 | PHA | Public Health Association |
 | PMA | Pharmaceutical Manufacturers Association |