Few therapeutic options are available for mucocutaneous leishmaniasis (MCL). We conducted a randomized open trial to evaluate the efficacy, safety, and tolerance of parenteral aminosidine sulphate (AS) 14 mg/kg/d for 21 days compared with intravenous meglumine antimonate (MA) 20 mg/kg/d for 28 days in patients with moderate MCL in Cuzco, Peru. Cure was defined as complete healing with re-epithelialization within 1 year of follow-up. The trial was stopped after 38 patients were enrolled (17 in the MA group and 21 in the AS group) because of marked differences in response. Study groups were comparable in baseline characteristics. Cure rates were 0/21 in the AS group compared with 8/17 (47%, 95% confidence interval: 23-71%) in the MA group (P < 0.001). Side effects and laboratory abnormalities were mild in both groups. We conclude that parenteral AS given on its own is not effective for MCL in Peru.