The cortex of Mimosa tenuiflora is a popular remedy utilized in Mexico for the treatment of skin lesions. Modern studies support the existence in this cortex of compounds with cicatrizing properties. In the present study the therapeutic effectiveness of an extract elaborated with this bark in the treatment of venous leg ulceration disease was explored. A randomized, double-blind, placebo-controlled clinical trial was conducted with ambulatory patients distributed into two groups, one receiving a hydrogel containing 5% of a crude extract standardized in its tannin concentration (1.8%), while the control group, was administered the same hydrogel but without addition of the extract. In both aseptic washings were performed initially followed by topical application of the corresponding hydrogel and dressing. Follow-up lasted 13 weeks and ulcer healing was determined through measurement of the lesion area by digital-photographic parameters. Therapeutic effectiveness occurred in all patients of the extract group; after the 8th treatment week, ulcer size was reduced by 92% as mean value in this group, whereas therapeutic effectiveness was observed only in one patient of the control group (chi(2), p=0.0001). No side effects were observed in any patient in either group.