OBJECTIVE: To describe the diagnosis of a patient with neonatal diabetes who had been misdiagnosed with type 1 diabetes and referred to our hospital for pancreas and kidney transplantation because of end-stage renal disease. RESEARCH DESIGN AND METHODS: A diagnosis of neonatal diabetes was made after a molecular genetic study revealed a mutation in exon 34 of the ABCC8 gene. Pancreas transplantation was ill-advised. RESULTS: The patient was switched from insulin to glibenclamide 4 months after kidney transplantation, confirming that pancreas transplantation would not have been a good decision. CONCLUSIONS: This is the first report of a patient with neonatal diabetes who developed diabetic nephropathy that progressed to end-stage renal disease. This report illustrates that careful endocrinological evaluation, including molecular genetic studies, if necessary, is mandatory before a decision to perform a pancreas transplant is made.