The results of a neurological, neuropsychological and MRI study of the brain in 21 patients (aged 18-59 years) with Sneddon's syndrome are reported. The predominant findings were marked neuropsychological deficits in two-thirds of the patients. While sensorimotor deficits after stroke in these patients had a good prognosis, neuropsychological deficits persisted. Of the 21 patients, 14 were incapable of gainful employment, 10 because of severe cognitive dysfunction.