The Coffin-Lowry syndrome (CLS) is a rare clinical entity where patients present with a characteristic facies, mental retardation and bone abnormalities. So far about 60 cases have been reported. Sensorineural hearing loss is not a characteristic symptom and a late-onset hearing loss has not been reported so far. We report on 4 brothers with CLS, aged 9-17 years, of whom 3 suffered from a severe sensorineural hearing loss with an onset during late childhood and adolescence after a normal hearing during early childhood. CT scans revealed no cochlear abnormalities. The boys were successfully equipped with hearing aids. It is suggested that in all CLS patients the hearing ability should be examined during early infancy and retested regularly in cases with normal hearing as these cases indicate that in CLS a late-onset hearing loss is possible during late childhood and adolescence.