Cerebral computed tomography was studied in eight patients with fetal methylmercury poisoning. All patients had evidence of prenatal exposure to methylmercury and showed psychomotor retardation. All of them had abnormal computed tomography findings. The most common finding was sulcal and ventricular enlargement, with or without cisternal enlargement. These findings indicated generalized cortical and subcortical maldevelopment. The distribution of sulcal and fissural enlargement did not show specific dominance in central sulcus, calcarine fissure or cerebellum. This distribution contrasts with the location of focal atrophy present in adult methylmercury poisoning. The computed tomography findings were relatively mild compared with the clinical features and were not distinct from those in cerebral palsy.