A
- 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
- 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
- Anaphylaxis
- Androgen insensitivity syndrome
- Angelman syndrome
- Angina
- Angioedema
- Angiography
- Animal and human bites
- Ankylosing spondylitis
- Anorexia nervosa
- 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
- Asthma
- Astigmatism
- Ataxia
- Atherosclerosis (arteriosclerosis)
- Athlete's foot
- Atopic eczema
- Atrial fibrillation
- Attention deficit hyperactivity disorder (ADHD)
- Auditory processing disorder (APD)
- Autism
- Autosomal dominant polycystic kidney disease
- Autosomal recessive polycystic kidney disease