| Abbreviations | Meaning |
 | 3-M [SYNDROME] | Initials For Miller, McKusick, And Malvaux, Who First Described The Syndrome |
 | 3C | 3-component; Cranio-cerebello-cardiac Syndrome |
 | 4H | Hypothalamic Hamartoblastoma-hyperphalangeal Hypoendocrine-hypoplastic Anus [syndrome] |
 | A(S) | Asplenia Syndrome |
 | AAA | Abdominal Aortic Aneurysm/aneurysmectomy; Acne-associated Arthritis; Acquired Aplastic Anemia; Acute Anxiety Attack; Alacrimia-achalasia-addisonianism [syndrome] |
 | AADH | Alopecia-anosmia-deafness-hypogonadism [syndrome] |
 | AAMS | Acute Aseptic Meningitis Syndrome |
 | AAS | Aarskog-Scott (syndrome) |
 | AAS | Acid Aspiration Syndrome |
 | AAS | Alcoholic Abstinence Syndrome |
 | AAS | Aarskog-Scott [syndrome]; Acid Aspiration Syndrome; Alcoholic Abstinence Syndrome; American Academy Of Sanitarians |
 | AAS | Aortic Arch Syndrome |
 | ABB | Albright-Butler-Bloomberg Syndrome |
 | ABB | Albright-Butler-Bloomberg [syndrome]; American Board Of Bioanalysis |
 | ABBQ | Acquired Immunodeficiency Syndrome Beliefs And Behavior Questionnaire |
 | ABL | Albright-Butler-Lightwood [syndrome]; Allograft-bound Lymphocyte; Angioblastic Lymphadenopathy |
 | ABMA | Anti-basement Membrane Antibody Disease (Goodpasture's Syndrome) |
 | ABS | Aging Brain Syndrome |
 | ABS | Abdominal Surgery; Acidic Ammonium Bisulfate; Acute Brain Syndrome; Adaptive Behavior Scale; Admitting Blood Sugar |
 | ABS | Amniotic Band Syndrome |
 | ABS | Antley-Bixler Syndrome |
 | ACD | Asymmetrical Cortical Degeneration Syndromes |
 | ACD | Adult Celiac Disease; Advanced Care Directive; Allergic Contact Dermatitis; Alopecia-contractures-dwarfism [syndrome] |
 | ACEDS | Angiotensin-converting Enzyme Dysfunction Syndrome |
 | ACHOO | Autosomal Dominant Compelling Helio-ophthalmic Outburst [syndrome] |
 | ACL | Acromegaloid Features, Cutis Verticis Gyrata, Corneal Leukoma (syndrome) |
 | ACL | Access Control List; Achievement Check List; Acromegaloid Features, Cutis Verticis Gyrata, Corneal Leukoma [syndrome] |
 | ACLS | Acrocallosal Syndrome; Advanced Cardiac Life Support; Assessment Of Children's Language Comprehension |
 | ACS | Acrocallosal Syndrome |
 | ACS | Acute Chest Syndrome |
 | ACS | Acute Coronary Syndrome |
 | ACTIS | [NLM DATABASE] Acquired Immunodeficiency Syndrome [AIDS] Clinical Trials Information Service |
 | ACTS | Acute Cervical Trauma Syndrome |
 | ACTS | Acute Cervical Traumatic Sprain Or Syndrome |
 | ADAM | Amniotic Deformity, Adhesion, Mutilation [syndrome] |
 | ADCS | Argonz Del Castillo Syndrome |
 | ADFN | Albinism-deafness [syndrome] |
 | ADOS | Autism Diagnostic Observation Scale; Autosomal Dominant Opitz Syndrome |
 | ADR | Ataxia-deafness-retardation [syndrome] |
 | ADS | Acute Death Syndrome; Acute Diarrheal Syndrome; Adenocarcinoma Dataset; Alcohol Dependence Scale; Alternative Delivery System |
 | ADS | Anatomical Dead Space; Anonymous Donor's Sperm; Antibody Deficiency Syndrome; Antidiuretic Substance; Army Dental Service |
 | AEC | Ankyloblepharon, Ectodermal Defects, And Cleft Lip [syndrome] |
 | AERS | Acute Equine Respiratory Syndrome |
 | AFA | Acromegaloid Facial Appearance [syndrome]; Advanced First Aid; Alcohol-formaldehyde-acetic Acid [fixative] |
 | AFIS | Amniotic Fluid Infection Syndrome |
 | AFRAX | Autism-fragile X [syndrome] |
 | AFS | Acquired Or Adult Fanconi Syndrome; Alternative Financing System; American Fertility Society; Antifibroblast Serum |
 | AGR | Aniridia-ambiguous Genitalia-mental Retardation [syndrome]; Anticipatory Goal Response |
 | AGS | Adrenogenital Syndrome; Alagille Syndrome; American Geriatrics Society; Audiogenic Seizures |
 | AHA | Anti-heart Antibody; Antihistone Antibody; Area Health Authority; Arthritis-hives-angioedema [syndrome]; Aspartyl-hydroxamic Acid; Autoimmune Hemolytic Anemia |