Primary testicular failure is characterized by low serum testosterone with appropriately high serum gonadotrophins, that is hypergonadotrophic hypogonadism. We report on a 27-year-old man with congenital adrenal hyperplasia (CAH) and infertility due to testicular adrenal rest rumours (TART) resulting in primary testicular failure but presenting with azoospermia, elevated serum testosterone and very low serum gonadotrophins. Hypergonadotrophic hypogonadism was unmasked by increasing glucocorticoid dosage. It is important to recognise the limitations of follicle-stimulating hormone, luteinising hormone and testosterone in assessing testicular function in men with CAH. Abnormal semen analysis may be the best indicator of testicular dysfunction in men with CAH.