CT scans on 110 children with a diagnosis of tuberous sclerosis have been compared with the clinical features of the disease. Patients with definite radiological as well as definite or suggestive clinical features accounted for only 80% of cases. 16% had positive radiological and negative clinical features and 4% had positive clinical and negative radiological features. There is little relationship between the mental development and the incidence of periventricular tubers or cortical and white matter lesions. In 15 patients older than 7 years the diagnosis was only made at the time of CT. Cerebral atrophy was not a prominent feature. Giant cell astrocytomas were present in 14%, one third of whom presented for the first time.