Congenital 21-alpha hydroxylase deficiency is a syndrome characterized by a cortisol synthesis deficiency and, rarely, by testicular masses. We present a case of bilateral nodular hyperplasia of the testis without adrenal hyperplasia in a patient affected by 21-alpha hydroxylase deficiency. This mass mimicked a testicular tumor and made differential diagnosis with a Leydig cell tumor extremely difficult. Multiple hard nodules (1 cm in diameter) could be palpated in both testes but were more prominent on the right. After an unsuccessful 30-day trial of an adrenocorticotropic hormone suppression regimen with dexamethasone (0.5 mg/qid), a right total orchifunicolectomy was performed. The final histological diagnosis was that of multiple, well-circumscribed nodules consisting of cord-like and microalveolar-like gonadal stroma, typical of an adrenogenital syndrome, and fibrosis. Differential diagnosis between testicular nodules in patients with congenital adrenal hyperplasia and Leydig cell tumors is a major clinical challenge. In cases of cortisol suppression resistant testicular masses, a serum adrenal hormone profile obtained from the gonadal vein and histology of the testicular nodule (with parenchyma sparing surgery) are recommended to obtain a correct diagnosis.