Background: To determine the effect of aspirin on ulcer healing rate in patients with chronic venous insufficiency, and to establish prognostic factors that influence ulcer evolution. Methods: Between 2001 and 2005, 78 patients with ulcerated lesions of diameter >2 cm and associated with chronic venous insufficiency were evaluated in our hospital. Of these, 51 patients (22 men, 29 women) with mean age of 60 years (range: 36e86) were included in a prospective randomized trial with a parallel control group. The treatment group received 300 mg of aspirin and the control group received no drug treatment; in both groups, healing was associated with standard compression therapy. During follow-up, held weekly in a blinded fashion, there was ulcer healing as well as cases of recurrence. Results were analyzed by intention-to-treat approach. Cure rate was estimated using KaplaneMeir survival analysis, and the influence of prognostic factors was analyzed by applying the Cox proportional hazards model. Results: In the presence of gradual compression therapy, healing occurred more rapidly in patients receiving aspirin versus the control subjects (12 weeks in the treated group vs. 22 weeks in the control group), with a 46% reduction in healing time. The main prognostic factor was estimated initial area of injury (P ¼ 0.032). Age, sex, systemic therapy, and infection showed little relevance to evolution. Conclusions: The administration of aspirin daily dose of 300 mg shortens the healing time of ulcerated lesions in the chronic venous insufficiency (CVI). The main prognostic factor for healing of venous ulcerated lesions is the initial surface area of the ulcer.