To investigate age-related differences in malignant hypertension (MHT), we studied 38 elderly patients (18 males, 20 females; mean age 70.6 years, SD 4.6 years, range 65 to 84) and 277 younger patients (193 males, 84 females; mean age 46.4 years, SD 10.5, range 15 to 64) with MHT presenting 1965-93. Mean duration of known hypertension before presentation was greater in the elderly group (43.8 months vs. 23.1 months). The elderly group included 18 (47.4%) newly diagnosed hypertensives, compared to 160 (55.8%) in the younger group. At presentation, 19 (50.0%) elderly patients were receiving no antihypertensive drug therapy, whilst 18 (47.4%) were taking one or more drugs for hypertension. Presenting clinical features in elderly MHT patients included visual disturbance (9), headaches (2), headaches with visual disturbance (2), stroke (3), and heart failure (2). Six patients were asymptomatic. The commonest clinical complications were ischaemic heart disease (angina and myocardial infarction) (5), heart failure (4) and stroke (4). The majority (58%) of patients, however, had no vascular complications at presentation. Comparing elderly and younger MHT groups, there was no significant difference in presenting systolic blood pressures, although mean diastolic blood pressure was significantly greater in the younger group (mean 143.7 mmHg +/- 19.3 vs. 130.0 mmHg +/- 15.2; p < 0.0001). After a mean follow-up of 30.9 months (SD 37.1; range 1 to 123 months), 17 (44.7%) of the elderly patients were still alive, 15 were dead (39.5%) and six were lost to follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)