OBJECTIVE To compare the effects and side-effects of polidocanol and tetracycline when used as sclerosants for testicular hydrocele and epididymal cyst. METHODS Forty-five men (median age 67 years, range 42-81) with 46 hydroceles or epididymal cysts were assessed. After puncture and aspiration, the empty sac was instilled with either polidocanol or tetracycline, assigned randomly. Patients recorded any treatment-associated pain on a visual analogue scale. RESULTS At 9 months of follow-up, nine of 17 men were cured after sclerotherapy with polidocanol compared with 17 of 20 men treated with tetracycline (P < 0.05). Tetracycline produced some pain for 3 days after treatment while polidocanol therapy was almost pain-free. Re-instillation should be considered for recurrences. At the follow-up after 35 months, 16 of 18 men treated with polidocanol and 20 of 22 men treated with tetracycline were satisfied with the outcome. CONCLUSIONS Both polidocanol and tetracycline are useful sclerosants for treating testicular hydrocele and epididymal cyst. We prefer polidocanol as a first choice in older patients because there were few short-term side-effects.