A 38-year-old woman had diffuse, nonnodular, lepromatous leprosy and Lucio's phenomenon. Most cases of Lucio's phenomenon have been reported to have a leukocytoclastic vasculitis as the underlying pathologic abnormality. In this patient, however, the histologic picture of an early lesion of Lucio's phenomenon showed a milk, mononuclear cell infiltration, endothelial swelling, vascular thrombosis, and ischemic necrosis. Lepra bacilli were abundant around nerves and blood vessels, and many were noted in vascular walls and endothelium. Our findings raise the possibility that some cases of Lucio's phenomenon may be caused by vascular damage due to direct invasion of Mycobacterium leprae and not necessarily by leukocytoclastic vasculitis.