Prophylactic cranial irradiation (PCI) has led to marked prolongation of survival, but also to intellectual and neuropsychological retardation in children with ALL. PCI has also been conducted in adult patients with small-cell bronchial carcinoma in the stage of minimal disease or with breast cancer. There are no studies assessing cognitive or other neuropsychological consequences of PCI in adult cancer patients. We report on a longitudinal prospective study of the effects of PCI on five major neuropsychological domains (intelligence, concentration, attention, memory and psychomotor performance). We report on our ongoing study, in which up to now 11 patients with small-cell lung cancer undergoing PCI have been investigated. Patients are assessed immediately before therapy started as well as 4 weeks and 3 months after onset of PCI. The used instruments are Standard Progressive Matrices (SPM), d2 Concentration Test, Minimental State, Verbal Learning Test and Psychomotor Tests (Steadiness, Aiming, Tapping, Tracking, Pursuit Rotor Test). Although our sample is small, results indicate that there is no evidence for a decrease in neuropsychological abilities in adults after three months. This is in contrast to the observed results after PCI in children. As compared to baseline measures, differences in memory, intelligence, concentration and attention were marginal over time. Moreover the progress of motor performance skills showed no clear tendency.