OBJECTIVE: Evaluation of school attainments in children with congenital hypothyroidism (CH) detected by neonatal screening and treated early in life. PATIENTS AND METHODS: Text comprehension, mathematics, reading, writing and verbal and spatial memory, as indices of school learning, were evaluated in nineteen 5- to 10-year-old children with CH attending nursery or elementary school. l-Thyroxine substitution (starting dose 8-10 microg/kg body weight per day) was initiated at a mean age of 30+/-10 days of life. The control group included 298 unaffected children matched with the CH children for age and school grade. Thirty per cent of controls were classmates of CH children. Intelligence quotients (IQ), language performances and motor development were evaluated in CH children at age 5 years, and were related to their school attainments. School performances of CH children were also compared with their neonatal serum thyroxine (T4) concentration, and with the social-cultural level of the family. RESULTS: Four out of 19 (21%) children with CH, 3 in the nursery and 1 in the elementary school, displayed a generalized learning disorder. Symbol copy, geometric copy, phrase repetition, dictation writing and spontaneous writing were particularly defective in nursery school CH children, while orthographic error recognition was defective in elementary school CH children. School learning disorders in CH children were significantly correlated with a borderline-low IQ, poor language performances and a low social-cultural level of the family, but not with motor skills or neonatal T4 concentration. CONCLUSION: School attainments of early treated CH children were within the normal range in most affected cases. However, about 20% of CH children, most of them attending nursery school, showed a generalized learning disorder. Low IQ scores and poor language performances at age 5 years were associated with defective learning, mainly in CH children living in a poor social-cultural environment. In this subset of CH children, prompt initiation of speech and psychomotor rehabilitation therapy is recommended in order to prevent subsequent school learning disorders.