| AA | Alcohol Abuse |
| AAAQ | Adult Asthma Adherence Questionnaire |
| AAD | Awful Agency Disease |
| AAFA | Asthma and Allergy Foundation of America |
| AAIC | Allergy Asthma Immunology Center |
| AAIO | Allergy Asthma Immunology Online |
| AAIR | Allergy Asthma Immunology of Rochester |
| AAIR | Allergy Asthma Immunology Rheumatology |
| AAOC | Altoona Arthritis and Osteoporosis Center |
| AASC | Allergy Asthma Sinus Center |
| ABCD | Advisory Board on Cat Diseases |
| ABDA | American Behcet's Disease Association |
| ABDA | Asian Breast Diseases Association |
| ABDF | Australasian Blistering Diseases Foundation |
| ACBS | Asthma Call back Survey |
| ACCD | Advisory Committee on Communicable Diseases |
| ACD | Anaemia of chronic disease |
| ACD | Anemia of Chronic Disease |
| ACDIP | Aging Chronic Disease and Injury Prevention |
| ACHD | Adult Congenital Heart Disease |