- Abdominal aortic aneurysm
- Abdominal pain
- Abortion
- Abscess
- Accidents and first aid
- Accidents to children in the home
- Acid reflux
- Acne
- Acoustic neuroma
- Actinomycosis
- Acupuncture
- Acute lymphoblastic leukaemia
- Acute myeloid leukaemia
- Addiction
- Addison's disease
- Adenoids and adenoidectomy
- ADHD
- Adhesive capsulitis
- Agoraphobia
- Air embolism
- Albinism (albino)
- Alcohol misuse
- Alcohol poisoning
- Alcoholic liver disease
- Allergic rhinitis
- Allergies
- Alopecia (hair loss)
- Altitude sickness
- Alzheimer's disease
- Ambiguous genitalia
- Amblyopia (lazy eye)
- AMD
- Amenorrhoea
- Amnesia
- Amniocentesis
- Amoebiasis
- Amputation
- Anabolic steroid abuse
- Anaemia, iron deficiency
- Anaemia, vitamin B12 or folate deficiency
- Anaesthesia
- Anal cancer
- Anal fissure
- Anal fistula
- Anal itching
- Anaphylaxis
- Androgen insensitivity syndrome
- Aneurysm, abdominal aortic
- Aneurysm, brain
- Anger management
- Angina
- Angioedema
- Angiography
- Angioplasty, coronary
- Ankle, broken
- Ankylosing spondylitis
- Anorexia nervosa
- Antacid medicines
- Antibiotics, macrolide
- Antibiotics, penicillins
- Anticoagulant medicines
- Antidepressants
- Antifungal medicines
- Antihistamines
- Anti-inflammatories, non-steroidal
- Antiphospholipid syndrome
- Antiplatelets, aspirin, low dose
- Antiplatelets, clopidogrel
- Anxiety
- Aortic valve replacement
- Aphasia
- Appendicitis
- Arm or elbow pain
- Arm, broken
- Arterial thrombosis
- Arteriography
- Arteriosclerosis
- Arthritis
- Arthroscopy
- Artificial insemination
- Asbestosis
- Asperger syndrome
- Aspergillosis
- Aspirin, low-dose
- Asthma in children
- Asthma
- Astigmatism
- Ataxia
- Atherosclerosis
- Athlete's foot
- Atopic eczema
- Atrial fibrillation
- Attention deficit hyperactivity disorder (ADHD)
- Audiometry
- Autism and Asperger syndrome
- Autopsy
- Autosomal dominant polycystic kidney disease (ADPKD)
- Autosomal recessive polycystic kidney disease (ARPKD)
- Avian flu (bird flu)
- Avian flu