- Achalasia
- Achilles tendon
- Achlorhydria
- Achondroplasia
- ACL
- Acne
- Acquired definition - HIV: health and medical information about HIV and AIDS
- Acquired immunodeficiency syndrome definition - HIV: health and medical information about HIV and AIDS
- Acquired mutation
- ACOG (Amer College of Ob & Gyn)
- Acrocentric chromosome
- Acrocyanosis
- Acrodermatitis enteropathica
- Acrodynia
- Acromegaly
- Actinic keratosis
- Activity, drug
- Active immunity
- Activities of daily living (ADLs)
- Acupuncture
- Acute
- Acute illness
- Acute leukemia
- ADA (American Diabetes Association) definition - Diabetes Mellitus, Type 2, Type 1, and Metabolic Disorders treatment and medications
- Adam's apple
- ADD (attention deficit disorder)
- Addison disease
- Adducted thumbs with mental retardation
- Adduction
- Adductor muscle
- Adenine (A)
- Adenocarcinoma definition - Lungs: pulmonary and respiratory health and medical information produced by doctors
- Adenoidectomy
- Adenoiditis
- Adenoids
- Adenoids and Tonsils
- Adhesion
- Adjuvant
- Adjuvant therapy
- ADLs (activities of daily living)