We reviewed the scrotal sonograms of 31 patients who had a testicular mass consisting of multiple small spherical or tubular anechoic structures in the region of the mediastinum testis. The median age of the patients was 62 years (range, 31-76 years). The abnormality was unilateral in 22 patients and bilateral in nine. Thirty-four (85%) of the 40 involved testicles had coexisting epididymal abnormalities: 32 with epididymal cysts and two with epididymitis. Follow-up sonograms were available in five patients and showed no change up to 4.5 years after the initial diagnosis. Surgical and histologic findings were available in one other patient and showed dilatation of the rete testis. The sonographic appearance and location of the lesions, the frequent presence of an epididymal abnormality, and the surgical and histologic findings in one case suggest that the lesion is due to dilatation of the rete testis, probably associated with obstruction in the epididymis. Recognition of this entity on sonograms may prevent unnecessary orchiectomy.