A spermatocele is a soft, fluctuant, and transilluminated epididymal cyst containing nonviable sperm in a milky fluid and located adjacent to the testis. It is usually over 2 cm in diameter. It is considered a benign and generally painless condition that does not impair fertility. Spermatoceles may be removed if they are very large or a cause of chronic pain, but they generally do not require treatment.

Spermatoceles occur in males and are often present at birth or in infancy. In utero exposure to a synthetic estrogen, diethylstilbestrol, is a known risk for the development of a spermatocele. This risk was recognized in the 1970s and 1980s, and diethylstilbestrol is now recognized as a category X medication.

Spermatoceles do not progress into testicular cancer. They do not strangulate or increase risk of vascular compromise to the testicles or surrounding structures.