O Lucio's phenomenon is an uncommon type 2 reactional state occurring exclusively in patients with diffuse lepromatous leprosy (Lucio-Latapi leprosy). Previous case reports have been most frequent in Central America and rare in Asia and Africa. Lucio's phenomenon is characterized by necrotic ulcerations of the skin preferentially on the lower extremities usually in association with ongoing Lucio lepromatosis. The purpose of this report is to describe an unusual case of Lucio's phenomenon occurring four years after successful treatment of diffuse lepromatous leprosy. The patient was a 51-year-old man who had presented diffuse lepromatous leprosy ongoing since 1998. Diagnosis was documented based on histological and bacteriologic evidence. After successful treatment using dapsone (100 mg/d), rifadine (600 mg/month) and ethionamide (250 mg/d), the patient was lost from follow-up for 4 years. In January 2005, he consulted again for alteration of general status. Clinical examination showed inflammatory livedo on the lower extremities in association with several infiltrating maculo-papular lesions and painful erythemato-pupuric lesions on the legs and buttocks. The patient's skin was dry, shiny and galabrous with alopecia of the eyelashes and eyebrows. Examination of smear samples (skin and nasal) to identify mycobacterium leprae was negative. Histological study demonstrated epidermic necrosis with aspects of leucocytoclastic vasculitis. No Virchow cells were detected and Ziehl staining was negative. Search for circulating immune complexes and antiphospholipid antibodies was negative. Diagnosis of Lucio's phenomenon was made and the patient was treated using prednisone at a dose of 1 mg/kg/d in association with rifampicine (600 mg/month) and dapsone (100 mg/d). Outcome was favorable after one month of treatment. Lucio's phenomenon has rarely been observed in Tunisia. To our knowledge this is the third case reported from Tunisia and only 13 cases have been reported in the world since 1983. In all cases including the two from Tunisia, Lucio's phenomenon occurred during the course of treatment of ongoing Lucio-Latapi lepromatous leprosy (2). The remarkable features of our case are that Lucio's phenomenon occurred a long time after successful treatment of lepromatous leprosy and that the patient responded promptly to treatment. The pathogenesis of Lucio's phenomenon is often compared with that of erythema nodosum leprosum. Discussion focuses on pathophysiologic features and natural course of Lucio's phenomenon.