The Wolfram, or DIDMOAD, syndrome consists of diabetes insipidus, diabetes mellitus, optic atrophy, and deafness. Diabetes mellitus usually occurs as the first manifestation of this syndrome, followed by the development of optic atrophy, neurosensory hearing loss, and finally diabetes insipidus. We report on four cases with a review of the literature. The diabetes mellitus occurring in these patients is clinically indistinguishable from classic type I diabetes mellitus. Two of three patients continue to have measurable C-peptide secretion 8 yr after onset of diabetes. Two of three patients with Wolfram syndrome had the HLA-DR2 antigen. Combining our cases with those described in the literature, 7 of 11 patients have the HLA-DR2 antigen. The preponderance of the HLA-DR2 antigen in the Wolfram syndrome is different from classic type I diabetes. This is further evidence of the genetic heterogeneity of diabetes mellitus. Although the Wolfram syndrome is rare, it should be considered in diabetic patients with unexplained optic atrophy and hearing loss or with polyuria and polydipsia in the presence of adequate blood sugar control.