- Abscess
- Achondroplasia
- Acne Rosacea
- Acne Vulgaris
- Acrocephalosyndactylia
- AIDS
- Acrodynia
- Acromegaly
- Actinic Keratosis
- Addison’s Disease
- Adenomatous Polyposis Coli
- Adie’s Syndrome
- Adiposis Dolorosa
- Adrenal Gland Diseases
- Agammaglobulinemia
- Aggression
- Aicardi Syndrome
- Airway Obstruction
- Alagille Syndrome
- Albinism
- Albinism, Ocular
- Albinism, Oculocutaneous
- Allergy
- Alopecia
- Alpha1 Antitrypsin Deficiency
- Alport’s Syndrome
- Altitude Sickness
- Amblyopia
- Amebiasis
- Amnesia
- Amniotic Band Syndrome
- Anemia, Aplastic
- Anemia, Hemolytic
- Anemia, Megaloblastic
- Anemia, Pernicious
- Anemia, Sickle Cell
- Anencephaly
- Aneurysm
- Angelman Syndrome
- Angina Pectoris
- Anisakiasis
- Anoxia
- Anthrax
- Anxiety Disorders
- Aortic Valve Stenosis
- Apert Syndrome
- Aphasia
- Apnea
- Appendicitis
- Apraxia
- Arachnoiditis
- (more Arachnoiditis)
- Arnold-Chiari Deformity
- Arrhythmia
- Arteriovenous Malformations
- Arthritis, Rheumatoid
- Arthritis
- Arthrogryposis
- Arthropathy, Neurogenic
- Arthropod Diseases
- Asperger’s Syndrome
- Ascites
- Asthma
- Astigmatism
- Ataxia
- Ataxia Telangiectasia
- Atelectasis
- Athetosis
- Attention Deficit Disorder with Hyperactivity
- Attention Deficit Disorders
- Attitude to Death
- Autism
- Arteriosclerosis
- Anemia
- Arrhythmogenic Right Ventricular Dysplasia
- Alzheimer’s Disease
- Autoimmune Diseases
- Autonomic Nervous System Diseases
- Avitaminosis