Hearing acuity was assessed in 45 children with sporadic congenital hypothyroidism during adequate long-term treatment. Otoscopy was performed in each and additional tympanometry in some of them. Secretory otitis media was found in 6 and was treated medically or by inserting grommets in the eardrum. In these children, hearing acuity was assessed after the otitis had been cured. Hearing acuity was measured either by conventional monoaural pure-tone audiometry (125-8000 Hz) or by binaural free field testing depending on the child's age (above and below 4 years respectively). Hearing was normal in 36 (80%) children. In the remaining 9, sensorineural hearing loss to some degree was detected affecting the higher frequencies in particular. Perceptive deafness required the use of a hearing aid in 4 children. No relationship could be found between hearing acuity and chronological age or bone age at diagnosis of congenital hypothyroidism or type of hypothyroidism. Sensorineural hearing loss is common in children with congenital hypothyroidism and should be searched for carefully and systematically to avoid difficulties related to speech and language development.