SummaryThe case of a patient with bilateral gynecomastia of 6 years duration is reported. The endocrine profile (high oestrogens, low testosterone and normal gonadotropin levels in plasma) was secondary to an abnormal oestrogen production from a testicular tumor, clinically not detectable but revealed by echography. The tumor was developed from the interstitial Leydig cells (leydigome) and showed no cytologic sign of malignancy; there were no detectable metastasis. After surgical removal of the testis with the tumor, a state of hypergonadotrophic hypogonadism developed, explaining the persistance of the gynecomastia and the moderate elevation of plasma oestrogens. It is probable that pre-existing testicular lesions are responsible for the persistance of the hypergonadotrophic hypogonadism in the postsurgical evolution.