Because of concern about deaths among diabetic patients using continuous subcutaneous insulin-infusion pumps, we conducted an investigation to determine whether the number of such deaths was excessive. By October 1982 we had identified 35 deaths among the estimated 3500 diabetic patients using pumps in the United States. The observed number of deaths was not greater than the expected number calculated from age-specific death rates for conventionally treated patients with Type I diabetes. The causes of death were not unusual, with two exceptions. One death was associated with malfunction of the device, and the other was attributed to acute bacterial endocarditis that arose from an abscess at the catheter-insertion site. Patients who died had high rates of autonomic neuropathy (66 per cent) and renal disease (39 per cent with serum creatinine levels above 5 mg per deciliter). We conclude that the use of continuous subcutaneous insulin-infusion pumps is not associated with excess mortality. However, certain types of patients may be at greater risk for death, and physicians should take great care in selecting patients for pump therapy.