- Dandruff
- De Quervain's tenosynovitis (hand tendon inflammation)
- Decompression sickness (bends, caisson's disease)
- Deep venous thrombosis (DVT, venous blood clot)
- Degenerative disc disease
- Dehydration
- Delirium tremens (“DTs”, severe alcohol withdrawal)
- Delusional disorder
- Dementia (decline in mental ability)
- Dengue fever (tropical mosquito borne illness)
- Dental abscess (tooth infection)
- Dental caries (cavities)
- Depression (excessive sadness)
- Dental eruption (appearance of new tooth)
- Dentures
- Detached retina (retinal detachment)
- Dermatofibroma
- Diabetes (high blood sugar)
- Developmental delay
- Diabetes mellitus type 1 (elevated blood sugar)
- Diabetes insipidus (excessive water loss from the kidneys)
- Diabetic ketoacidosis (DKA, a complication of poorly controlled diabetes)
- Diabetes mellitus type 2 (elevated blood sugar)
- Diabetic nephropathy (diabetes and kidney disease)
- Diabetic neuropathy (nerve damage)
- Diabetic retinopathy (diabetic eye disease)
- Diaper rash
- Diastema (gap between teeth)
- Difficulty swallowing (dysphagia)
- Diffuse esophageal spasm (painful contractions of the esophagus)
- Diphtheria infection (bacterial respiratory infection)
- Discitis (spinal disk inflammation)
- Discoid Lupus Erythematosus (DLE, autoimmune skin inflammation)
- Dislocated lens (eye disorder)
- Dislocation (joint out of place)
- Dislocation of the temporomandibular joint
- Dissecting aortic aneurysm (tearing and dilation of the aorta)
- Disseminated intravascular coagulation (DIC, abnormality of blood clotting)
- Diverticulosis (weakening of the large intestine wall)
- Dog bite
- Double diabetes (hybrid diabetes)
- Down syndrome (common genetic disorder)
- Dressler syndrome (heart sac inflammation following heart attack or heart surgery)
- Drug overdose
- Drug overuse
- Drug reaction
- Drug withdrawal syndrome
- Dry air nasal irritation
- Dry eye syndrome (eye disorder)
- Dry socket (pain after tooth removal)
- Ductal carcinoma in situ (DCIS, breast cancer)
- Duodenal cancer (small intestine)
- Dupuytren's contracture (contracted palmar fascia)
- Dysfunctional uterine bleeding (abnormal vaginal bleeding)
- Dysgeusia
- Dyslexia (reading disorder)
- Dyslipidemia (abnormal fat levels in the blood)
- Dysthymia (depression, dysthymic disorder)
- Dystonia