In adult patients with congenital adrenal hyperplasia (CAH) the presence of testicular adrenal rest tumours (TART) is an important cause of gonadal dysfunction and infertility. In the last decade several papers have focused on the origin and pathogenesis of these tumours. In this paper we review the embryological, histological, biochemical and clinical features of TART and discuss the treatment options. Furthermore, we propose a new five-stage classification of TART, based on sonographic, clinical and biochemical parameters, that may lead to a better follow up and treatment of patients with TART.