Background: Hydrocele is an abnormal collection of serous fluid in the tunica vaginalis. The most common form of hydrocele in adults is primary or idiopathic, affecting approximately 1% of adult men. Most patients receive surgical treatment. We report a case cured by intracapsular injection of polidocanol. Case summary: A 32-year-old man found a lump in his left scrotum while taking a bath. He conducted a transillumination test himself, and the result was positive. Hydrocele of the testis was then diagnosed by ultrasound examination. The patient underwent several rounds of hydrops aspiration, intracapsular drug injection, and oral antibiotic treatment, but all failed. Finally, the hydrocele was cured by injection of polidocanol into the capsule. Conclusion: Simple hydrocele aspiration and intracapsular injection of anti-inflammatory drugs had no obvious therapeutic effect. Intracapsular injection of polidocanol has a reliable and lasting therapeutic effect on hydroceles with the advantages of procedure simplicity, low cost, rapid recovery, and few side effects.