Patient data obtained from the cystic fibrosis clinic of the Hospital for Sick Children (Toronto, Canada) over the period 1977 to 1988 were analyzed to compare the diabetic and nondiabetic cystic fibrosis patients. The pulmonary function, nutritional status, and survival data for 713 patients who attended the clinic over the 11-year period are reported. Insulin-dependent diabetes was found to exist in 37 (5.2%) of 713 patients. The patient age at time of diabetes diagnosis ranged from 2 to 34 years, with a mean +/- SD of 20.0 +/- 7.4 years. Patients who died in both the diabetic and nondiabetic groups had worse pulmonary and nutritional status than the surviving patients, but there were no significant differences between the diabetic and nondiabetic groups in those who died or in those who remained alive. Survival analysis showed a similar prognosis in the diabetic and nondiabetic groups. It is concluded that cystic fibrosis patients with diabetes are, for their age, not different from patients without diabetes with respect to pulmonary function, nutritional status, and survival.