Three cases of insulin-requiring diabetes mellitus associated with tacrolimus (FK506) therapy in pediatric renal transplant patients are presented. New-onset diabetes mellitus has been reported with tacrolimus therapy post liver and kidney transplants in up to 12% of adult patients, but is thought to be rare in pediatrics. Although insulin requirement with tacrolimus therapy has been occasionally reported in adolescent patients post liver transplant, only a single case in a pediatric kidney transplant recipient has been previously documented. These cases illustrate the significant diabetogenic effect of tacrolimus in pediatric renal transplant patients. As the use of tacrolimus becomes more prevalent in pediatric kidney transplantation, pediatric nephrologists should be aware of this potential complication.