Three siblings from consanguineous parents, originating from Tanzania, presented with symptoms of complete or partial agenesis of the corpus callosum. Two males had in addition a sensorimotor neuropathy, moderate mental retardation and skeletal dysmorphism (Andermann syndrome). A study of sural nerve biopsies revealed thickening of the perineurium and reduction in the number of large myelinated fibres with axonal degeneration. Muscle biopsies showed neurogenic atrophy. The Andermann syndrome is autosomal recessive and almost exclusively confined to the region of Charlevoix and Saguenay-Lac-St-Jean (Quebec, Canada). Moreover in families with the Andermann syndrome, no siblings with only agenesis of the corpus callosum have been described.