Wolfram syndrome (MIM 222300) is the association of juvenile onset diabetes mellitus and optic atrophy, also known as DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness). Patients present with diabetes mellitus followed by optic atrophy in the first decade, cranial diabetes insipidus and sensorineural deafness in the second decade, dilated renal outflow tracts early in the third decade, and multiple neurological abnormalities early in the fourth decade. Other abnormalities include primary gonadal atrophy. Death occurs prematurely, often from respiratory failure associated with brainstem atrophy. Most patients eventually develop all complications of this progressive, neurodegenerative disorder. The pathogenesis is unknown, but the prevalence is 1 in 770000 in the UK and inheritance is autosomal recessive. A Wolfram gene has recently been mapped to chromosome 4p16.1, but there is evidence for locus heterogeneity, and it is still possible that a minority of patients may harbour a mitochondrial genome deletion. The best available diagnostic criteria are juvenile onset diabetes mellitus and optic atrophy, but there is a wide differential diagnosis which includes other causes of neurodegeneration.