A retrospective study of the neurological problems arising in HIV-I seropositive patients in a single defined geographical area was undertaken. Ninety patients were referred for a neurological opinion from a total known HIV-I seropositive population of 436. Minor problems were frequently encountered early in the course of disease (20 at CDC stage II, 12 at CDC stage III), including seizures related to drug abuse in six. The most frequent neurological problem in those patients in CDC group IV (58 patients) were the AIDS dementia complex (14 patients), an axonal sensorimotor neuropathy (12), toxoplasmosis (nine) and cryptococcal meningitis (three). All patients with a structural lesion had appropriate focal signs on examination. The value and role of CT cranial scanning in the diagnosis of toxoplasmosis is discussed and the importance of recognizing potentially treatable causes of both intellectual impairment and cytomegalovirus-related neuropathies is stressed. This is the first report of an unselected series of patients at all stages of HIV-I related neurological disease from a single UK centre.