Lucio's phenomenon is defined as a variant of type 2 leprosy reaction. It is a 
rare event, occurring in the evolution of leprosy of Lucio and other forms of 
lepromatous leprosy. It has an exacerbated proliferation of Hansen bacilli in 
its pathophysiology, which invade blood vessel walls and injure endothelial 
cells, causing endothelial proliferation and decreasing the vascular lumen. This 
fact, associated with inflammatory reactions and changes in the coagulation 
system causes vascular thrombosis, ischemia, infarction and tissue necrosis, 
leading to the histopathological characteristic of the phenomenon. We report a 
case of lepromatous leprosy with irregular treatment that developed Lucio's 
phenomenon. Treatment with multidrug therapy, antibiotics, steroids and 
thalidomide achieved a favorable outcome.