Ataxia-telangiectasia, an autosomal recessive disorder caused by defect of the ataxia-telangiectasia mutated gene, is characterized by progressive neurologic impairment with cerebellar atrophy, ocular and cutaneous telangiectasia, immunodeficiency, heightened sensitivity to ionizing radiation and susceptibility to developing lymphoreticular malignancy. Supratentorial brain abnormalities have been reported only rarely. In this study, brain MRI was performed in 10 adults with ataxia-telangiectasia having stable neurologic impairment. Intracerebral telangiectasia with multiple punctate hemosiderin deposits were identified in 60% of subjects. These lesions were apparently asymptomatic. They are similar in appearance to radiation-induced telangiectasia and to cryptogenic vascular malformations. Also noted, in the 2 oldest subjects, was extensive white matter T2 hyperintensity, and in 1 of these a space-occupying fluid collection consistent with transudative capillary leak and edema as evidenced by reduced levels of metabolites on MR spectroscopic imaging. Asymptomatic supratentorial vascular abnormalities appear to be common in adults with ataxia-telangiectasia.