Neuropsychologic tests were performed in 40 children with acute lymphoblastic leukemia. They all had been treated at a young age with systemic chemotherapy, cranial irradiation and intrathecal methotrexate. The test results showed a high risk for learning disabilities. Visual motor integration problems were present early after cessation of treatment, but most cognitive defects became apparent about 2 years after stopping therapy. At that time 23% (9/40) of the children required special school types and 30% (12/40) needed additional help within their residential school. Problems with arithmetic were most prominent. Future study of patients who did not receive prophylactic irradiation of the brain will help to clarify the potential causative role of cranial irradiation in these cognitive defects.