A study has been made to assess the incidence of hypertension in patients who have suffered an episode of renal trauma sufficiently severe to cause haematuria. Sixty-three patients were studied and 63 age- and sex-matched controls were also studied. At follow-up, 6-138 months after injury, 13 of the patients who had suffered renal trauma and 12 of the control subjects had a diastolic blood pressure above 99 mm Hg. Three patients showed significant reduction in the size and volume of the previously damaged kidney. In this group, renal trauma did not appear to be associated with an increased risk of permanent hypertension.