The aim of the present study was to elucidate the role of the cerebellar hemispheres in executive functions. The findings are relevant because of the large number of children who survive cerebellar tumors. Neuropsychologic assessments of four patients (8-21 years of age) who had undergone neurosurgery for removal of tumors in the cerebellar hemispheres were conducted and compared with the assessments of six children who had been diagnosed with temporal lobe tumors or cysts. The executive functions were assessed using the Wisconsin Card Sorting Test. IQs were average in both groups. As expected, patients with cerebellar hemispheric lesions had impaired executive functions. In particular, they appeared to have difficulty generating and testing hypotheses regarding the matching rules on the Wisconsin Card Sorting Test. Patients with temporal lesions had a different pattern of deficits on this test. The findings are consistent with the theories that propose that the cerebellar hemispheres are involved in cognitive processes. The findings also demonstrate that subtle deficits in executive functions can be masked by a normal IQ in survivors of cerebellar tumors and highlight the need to design interventions targeted toward problem-solving skills. (C) 2000 by Elsevier Science Inc.