Identifying cognitive deficits associated with pediatric brain tumors and their treatment is important in delineating the mechanisms of intellectual decline often associated with these diseases. The authors evaluated sustained attention, information processing speed, working memory, and IQ in 64 patients with posterior fossa tumors, including those treated with either: (a) surgery and cranial radiation (n = 32), and (b) surgery without radiation (n = 32). Ten patients treated for non-CNS solid tumors were included as a comparison group. The authors also examined the impact of relevant demographic and medical variables on neurocognitive outcome. The authors found that neither age at, nor time since, diagnosis predicted cognitive outcome in this sample. Further, sustained attention and working memory were largely intact and there were no differences between groups. Patients treated with cranial radiation demonstrated lowered short-form IQ and slow information processing speed: Patients treated with cranial radiation and who experienced postsurgical complications demonstrated the poorest performance. The authors consider information processing speed to be an excellent candidate mechanism in understanding the impact of cranial radiation on intellectual outcome.