Despite mounting experimental evidence that cyclosporine inhibits pancreatic islet cell function, clinical data on posttransplant diabetes mellitus (PTDM) in renal allograft recipients in the cyclosporine era are scarce. Between June 1983 and December 1988, 39 of 337 (11.6%) cyclosporine-treated adult renal transplant recipient whose grafts survived longer than 1 year developed PTDM. Of these, 43.6% and 74.4% were diagnosed by 3 and 12 months posttransplant, respectively, and 51.3% were insulin-dependent. Incidence of PTDM was highest in blacks (19.8%) and Hispanics (21.3%) and in those with HLA-A 30 and Bw 42 antigens. Older recipients and those that received cadaveric kidneys were more likely to develop diabetes than those who received living related allografts (14% vs. 5.3%, P less than 0.05). The rate of PTDM appeared to be independent of the type of induction, immunosuppressant therapy, incidence of rejection, total steroid and cyclosporine dose, percentage of body weight gain in the first posttransplant year, and serum creatinine concentration. Actuarial 5-year, decaying from 100% at 1 year, patient and graft survival rates were 87% and 70%, respectively, in the PTDM group compared with 93% and 90%, respectively, in controls. Causes of graft failure among the diabetics included chronic rejection (6), patient death (3), noncompliance with immunosuppressants (2), and sepsis (1). The incidence of infectious complications was significantly higher in the PTDM group compared with the control group (53% vs. 16%, P less than 0.05), with all 5 deaths among the diabetics being sepsis-related.