Wolfram syndrome is a rare, autosomal recessive disorder characterized by early-onset diabetes mellitus, optic atrophy and neurological and endocrinological abnormalities. A 47-year-old Japanese man with frequent severe hypoglycemic episodes was diagnosed as Wolfram syndrome based on clinical features and laboratory data. He had positive glutamic acid decarboxylase (GAD) and insulinoma-associated antigen-2 (IA-2) antibodies, both uncommon in this syndrome. Genetic analysis revealed that WFS1 gene of the patient has a homozygous 5 base pairs (AAGGC) insertion at position 1279 in exon 8, causing a frameshift at codon 371 leading to premature termination at codon 443.