Diagnosaurus
- Abdominal aortic aneurysm
- Abortion, recurrent
- Abortion, spontaneous
- ABPA
- Abscess, liver
- Acanthosis nigricans
- Acetaminophen poisoning
- Achalasia
- Acidosis, lactic
- Acidosis, metabolic, increased anion gap
- Acidosis, metabolic, normal anion gap
- Acidosis, renal tubular
- Acidosis, respiratory
- Acne rosacea
- Acne vulgaris
- Acromegaly
- Actinic keratoses
- Actinomycosis
- Acute intermittent porphyria
- Acute lymphocytic leukemia
- Acute myelogenous leukemia
- Acute respiratory distress syndrome
- Acute tubular necrosis
- Addison's disease
- ADH, syndrome of inappropriate
- Adjustment disorder
- Adrenal insufficiency, acute
- Adrenal insufficiency, chronic
- Adult Still's disease
- Aggressive behavior
- Agoraphobia
- AIDS & HIV
- AIDS and renal failure
- Airway obstruction, bronchi
- Airway obstruction, trachea
- Airway obstruction, upper
- Alcohol dependence
- Alcoholic hepatitis
- Alcohol withdrawal
- Aldosterone excess
- Alkalosis, metabolic
- Alkalosis, respiratory
- ALL
- Allergic bronchopulmonary aspergillosis
- Allergic rhinitis
- Alopecia
- Altitude sickness
- Alveolar hemorrhage
- Amaurosis fugax
- Amebiasis
- Amenorrhea, primary
- AML
- Amphetamines intoxication
- Amyloidosis
- Anal fissure
- Anaphylaxis
- Anemia, aplastic
- Anemia, general approach
- Anemia, hemolytic
- Anemia, iron-deficiency
- Anemia, macrocytic
- Anemia, microcytic
- Anemia, normocytic
- Anemia, sickle cell
- Anemia of chronic disease
- Aneurysm, abdominal aortic
- Aneurysm, carotid artery
- Aneurysm, thoracic aortic
- Angina pectoris
- Angioedema
- Angular cheilitis
- Anion gap, decreased
- Anion gap, increased
- Ankylosing spondylitis
- Anogenital pruritus
- Anorectal pain
- Anorexia nervosa
- Anosmia
- Anovulation in reproductive years
- Anthrax
- Antibiotic-associated colitis
- Anticholinergic poisoning
- Anti-GBM disease
- Aorta, coarctation
- Aortic aneurysm, abdominal
- Aortic aneurysm, thoracic
- Aortic dissection
- Aortic insufficiency
- Aortic stenosis
- Aphthous ulcer
- Aplastic anemia
- Appendicitis
- ARDS
- Arm ischemia
- Arthritis, acute, multijoint
- Arthritis, acute, one joint
- Arthritis, chronic, multijoint
- Arthritis, chronic, one joint
- Arthritis, degenerative
- Arthritis, general DDx
- Arthritis, gonococcal
- Arthritis, psoriatic
- Arthritis, reactive
- Arthritis, rheumatoid
- Arthritis, septic (nongonococcal)
- Arthritis & inflammatory bowel disease
- Arthropods causing skin lesions
- Asbestosis
- Ascariasis
- ASD
- Aspergillosis
- Aspirated foreign body
- Aspiration of gastric contents, chronic
- Asplenia and infection risk
- Asthma
- Athlete's foot
- ATN
- Atopic dermatitis
- Atrial fibrillation
- Atrial flutter
- Atrial myxoma
- Atrial septal defect
- Atrioventricular block
- Atropine poisoning
- Auditory tube dysfunction
- Auricle diseases
- Autonomic insufficiency
- Avascular necrosis
- AVN