• Abdominal aortic aneurysm

• Abdominal aortic aneurysm screening

• Abortion

• Abscess

• Acanthosis nigricans

• Achalasia

• Acid and chemical burns

• Acne

• Acoustic neuroma (vestibular schwannoma)

• Acromegaly

• Actinic keratoses (solar keratoses)

• Actinomycosis

• Acupuncture

• Acute cholecystitis

• Acute kidney injury

• Acute lymphoblastic leukaemia

• Acute myeloid leukaemia

• Acute pancreatitis

• Acute respiratory distress syndrome

• Addison's disease

• Adenoids and adenoidectomy

• Age-related cataracts

• Age-related macular degeneration (AMD)

• Agoraphobia

• Air or gas embolism

• Albinism

• Alcohol misuse

• Alcohol poisoning

• Alcohol-related liver disease

• Alexander technique

• Alkaptonuria

• Allergic rhinitis

• Allergies

• Altitude sickness

• Alzheimer's disease

• Amniocentesis

• Amputation

• Amyloidosis

• Anabolic steroid misuse

• Anaesthesia

• Anal cancer

• Anal fissure

• Anal fistula

• Anal pain (proctalgia)

• Anaphylaxis

• Androgen insensitivity syndrome

• Angelman syndrome

• Angina

• Angioedema

• Angiography

• Animal and human bites

• Ankylosing spondylitis

• Anorexia nervosa

• Anosmia

• Antacids

• Antibiotics

• Anticoagulant medicines

• Antidepressants

• Antifungal medicines

• Antihistamines

• Antiphospholipid syndrome (APS)

• Antisocial personality disorder

• Anxiety disorders in children

• Aortic valve replacement

• Aphasia

• Appendicitis

• Arrhythmia

• Arterial thrombosis

• Arthritis

• Arthroscopy

• Asbestosis

• Aspergillosis

• Aspirin

• Asthma

• Astigmatism

• Ataxia

• Atherosclerosis (arteriosclerosis)

• Athlete's foot

• Atopic eczema

• Atrial fibrillation

• Attention deficit hyperactivity disorder (ADHD)

• Auditory processing disorder

• Autism

• Autosomal dominant polycystic kidney disease

• Autosomal recessive polycystic kidney disease