In untreated congenital adrenal hyperplasia due to 21-hydroxylase deficiency (21OHDS) the presence of adrenal and testicular tumors had been described; however little is known about the effect of the enzymatic defect on fertility in males. We studied a male adult patient affected by 21OHDS for infertility, after a long period of discontinuation of glucocorticoid therapy and then during resumption of treatment and 8 months after monoadrenalectomy. The initial spermatic count revealed azoospermia and testicular needle aspiration showed a cytological picture consistent with prepuberty. The morphofunctional study revealed a right adrenal mass with reduced uptake at radioscan. Treatment was resumed with onset of impotency, which improved after reduction of the dose of glucocorticoids. The patient was monoadrenalectomised and his spermatic count increased. The patient shows that corticosteroid therapy in 21OHDS should be continued lifelong to avoid adrenal hyperplasia with possible areas of autonomy and to allow regular fertility. Impotence during treatment is probably due to a decrease of excessive adrenal androgens while testicular androgen production is still suppressed.