Congenital adrenal hyperplasia results from an adrenal enzyme deficiency, that causes an underproduction of glucocorticoids and sometimes mineralocorticoids and a resultant overproduction of androgens, until treatment with replacement glucocorticoids is instituted. The goal of this study was to determine the frequency and etiology of white-matter changes and temporal lobe atrophy demonstrable on magnetic resonance imaging (MRI) in a group of children and young adults with congenital adrenal hyperplasia. About one third of the patients evidenced white-matter abnormalities or temporal lobe atrophy. All patients, except one with a known stroke, had normal neurologic examinations. Exposure to excess exogenous glucocorticoids in the process of being treated for congenital adrenal hyperplasia is the most theoretically appealing explanation for these MRI findings. However, the relationship of MRI findings to treatment status (over-versus under-suppressed) does not run in clear parallel.