The purpose of the present study was to define the late effects, both physical and psychological, of treating low-grade astrocytomas with radiotherapy. Fifty patients, half of whom received radiotherapy, underwent an assessment of neurological and neuropsychological function. There was no difference in neurological function between the two groups. The radiotherapy recipients, including those with cerebellar tumours, performed significantly worse on measures of intelligence and information processing. In addition, there was a greater incidence of special education needs in the irradiated group. We conclude that children with low-grade astrocytomas who receive radiotherapy have no greater neurological deficit but that the use of radiotherapy carries a penalty in terms of long-term cognitive function and confirmed the findings of many previous reports that supratentorial irradiation is detrimental. More surprisingly, it has been demonstrated that local field irradiation to the posterior fossa can also produce significant cognitive impairment.