A randomized, open, controlled clinical trial was designed to evaluate the efficacy, tolerance, and safety of sodium stibogluconate plus allopurinol and sodium stibogluconate alone as treatment of patients with mucocutaneous leishmaniasis. In phase 1 of the study, all 22 patients with severe disease had improvement of their lesions, but only two had clinical cure (both of these patients received sodium stibogluconate alone). In phase 2, which included 59 patients with moderate disease, the cure rate among sodium stibogluconate recipients was 75% (21 of 28) compared with 63.6% (14 of 22) among the sodium stibogluconate plus allopurinol recipients. The rates of clinical adverse events were similar among both groups. Thrombocytopenia was more frequent in the sodium stibogluconate plus allopurinol recipients, but the difference was not statistically significant. Eight patients (two sodium stibogluconate recipients and six sodium stibogluconate plus allopurinol recipients) withdrew from the study because of severe thrombocytopenia. In this study, the addition of allopurinol to sodium stibogluconate provided no clinical benefit as treatment of mucocutaneous leishmaniasis.