BACKGROUND Topical spironolactone may be effective for the treatment of acne patients with increased sebum secretion. OBJECTIVE To evaluate the efficacy of 5% spironolactone gel in the treatment of mild to moderate acne vulgaris. METHODS This study was a double-blind clinical trial, performed randomly in two demographically equivalent groups. In this study, 78 patients with mild to moderate acne vulgaris participated. The patients, as groups of cases (38 patients) and controls (40 patients), took 5% spironolactone gel and placebo, respectively. The response to treatment was evaluated by the total acne lesions (TLC) and acne severity index (ASI). RESULTS The mean age of the case patients was 21.5 ± 4.2 years and of the control patients was 22.2 ± 4.06 years. The difference in TLC was statistically significant between the two groups (p = 0.007), but no statistically significant difference was seen between the two groups for ASI (p = 0.052). CONCLUSION The 5% spironolactone topical gel resulted in a decrease in the TLC in acne vulgaris, while it had no significant efficacy in the ASI.