A 17-year-old boy with a history of classic congenital adrenal hyperplasia (CAH) secondary to 21-α hydroxylase deficiency on treatment with hydrocortisone and fludrocortisone presented to the endocrinology clinic with bilateral painful testicular masses. Previous urologic evaluation revealed no evidence of hydrocele or epididymitis. Semen analysis showed azoospermia. Physical examination demonstrated Tanner stage V and normal phallus; the left testicle measured approximately 8 cm, and the right testicle measured 7 cm in largest diameter (Fig. 1 and 2). Laboratory evaluation showed the following: (1) alfa-fetoprotein level, 1.4 (reference range, 0.0-10.0) ng/mL; (2) human chorionic gonadotropin level, <0.1 (reference range, 0.0-1.0) mU/mL; (3) total testosterone level, 541 (reference range, 250-1100) ng/dL; (4) follicle-stimulating hormone level, 11.4 (reference range, 1.5-12.4) mU/mL; (5) luteinizing hormone level, 1.7 (reference range, 1.7-11) mU/mL; (6) adrenocorticotropic hormone level, 86 (reference range, 6-50) pg/mL; and (7) inhibin A level, <1 (reference range, <21) pg/mL.Fig. 2The left testicle measuring approximately 8 cm in largest diameter.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Scrotal ultrasound revealed markedly enlarged testes (60 mL and 70 mL) with hyperemia and no discrete masses, findings consistent with testicular adrenal rest tumor (TART) (Fig. 3). Partial orchiectomy confirmed the diagnosis. TARTs are firm bilateral painful masses originating near the rete testes developed in men with poorly controlled classic 21-α hydroxylase deficiency under the influence of chronically elevated adrenocorticotropic hormone levels. In recent studies, an overall prevalence of 40% (14%-89%) has been reported in patients with classic CAH.1Engels M. Span P.N. van Herwaarden A.E. Sweep F.C.G.J. Stikkelbroeck N.M.M.L. Claahsen-van der Grinten H.L. Testicular adrenal rest tumors: current insights on prevalence, characteristics, origin, and treatment.Endocr Rev. 2019; 40: 973-987Crossref PubMed Scopus (53) Google Scholar Ultrasonography is the most sensitive method of diagnosis. This condition is the most common cause of infertility in male patients with CAH. Although surgery can relieve the pain associated with the mass, it does not lead to increased testosterone production and improved fertility. Intensified glucocorticoid therapy is sometimes, but not always, effective in decreasing TART size and restoring fertility.2Claahsen-van der Grinten H.L. Otten B.J. Stikkelbroeck M.M. Sweep F.C. Hermus A.R. Testicular adrenal rest tumours in congenital adrenal hyperplasia.Best Pract Res Clin Endocrinol Metab. 2009; 23: 209-220Crossref PubMed Scopus (111) Google Scholar Routine physical examination along with annual ultrasound screening is recommended for early detection of the disease. The importance of good medication compliance was discussed with the patient, and the dosage of glucocorticoids was increased. The plan was to proceed with microdissection of testicular sperm extraction with cryopreservation in case fertility is not achieved by medical approach. The authors have no multiplicity of interest to disclose.