Lipomembranous fat necrosis (LMFN) is a special subtype of fat necrosis characterized by the development of pseudocystic cavities lined with hyaline-crenulated membranes. This regressive degeneration or localized destruction of adipose tissue has been reported as a focal phenomenon or, rarely, as an extensive one in several pathologic conditions of the subcutaneous tissue. LMFN is frequently observed in patients who have chronic sclerotic infiltrated plaques or tender subcutaneous nodules on the lower extremities, often diagnosed as lipodermatosclerosis. There is increasing evidence that it is a morphologic feature that cannot be related to any particular clinical setting, however. Multiple local or systemic events causing a compromise in the blood supply of the subcutaneous tissue have been incriminated. The current knowledge of the different disorders associated with LMFN is reviewed. The different postulated pathogenic mechanisms leading to LMFN are also discussed.