A 31-year-old man with left-sided testicular pain lasting a couple of months was referred to our urology department due to a suspected testicular tumor. Physical examination showed a hard, thickened, and small left testis on palpation with a diffuse, inhomogeneous ultrasonographic appearance. After a urologic examination, a left-sided inguinal orchiectomy was performed. The testis, epididymis, and spermatic cord were sent to pathology. Gross examination revealed a cystic cavity filled with brown fluid and the surrounding brownish parenchyma measuring up to 3.5 cm in diameter. Histologic examination showed a cystically dilated rete testis lined with cuboidal epithelium and a positive immunohistochemical reaction to cytokeratins. Microscopically, the cystic cavity was a pseudocyst filled with extravasated erythrocytes and abundant clusters of siderophages. The siderophages extended into the testicular parenchyma, surrounding the seminiferous tubules and spreading out around the ducts of the epididymis, which were also cystically dilated with siderophages inside their lumina. On the basis of clinical data, histological, and immunohistochemical analysis, the patient was diagnosed with cystic dysplasia of the rete testis. The literature shows an association between cystic dysplasia of the rete testis and ipsilateral genitourinary anomalies. Therefore, our patient underwent a multi-slice computed tomography scan, which revealed ipsilateral renal agenesis, a right seminal vesicle cyst reaching up to the iliac arteries, and a multicystic formation cranial to the prostate. Cystic dysplasia of the rete testis is a rare, benign cause of testicular mass, mostly observed in children. Around 60 cases have been recorded since the initial description in 1973 (1). Cystic dysplasia of the rete testis is characterized by irregular cystic areas lined by cuboidal epithelium in the mediastinum or rete testes. It frequently coexists with genitourinary tract abnormalities, most prominently renal agenesis (2). Only two adult patients, aged 23 and 63, have been reported in the literature so far.