The anterolateral thigh flap was first described by Song in 1984 and became popular during last decade. This flap is usually nourished by 1 or 2 perforator vessels. No previous studies described the microscopic anatomy of these perforators or the possible degenerative changes that it may present. The aim of this study was to describe the microscopic anatomy and degenerative changes found in cadaver dissections. Twenty-nine anterolateral thigh flaps were dissected on 16 fresh cadavers. At the level of muscular fascia two samples of perforator vessels with 1.5 cm long, were harvested and fixed with formalin. Five millimeters sections of paraffin-embedded tissue were stained with hematoxilin-eosin, Verhoeff and Picrosirius. Histological degenerative changes were evaluated and histomorphometric measurements were made. Data were analyzed with a computer assisted device with OptimasŪ software. The mean microscopic external diameter of perforator arteries was 0.52mm (+/-0.2mm). In 44,8% major degenerative changes were found, including moderate/ severe intimal layer proliferation, moderate/ severe medial layer fibrosis or calcification. Minor degenerative changes were not included in this study. The small size external diameters with a high standard deviation found in measurements are similar to surgical findings. A great number of moderate/ severe degenerative changes were observed which could explain a number of flap failures when an adequate microsurgical technique is applied. However comparative clinical studies must be done to elucidate the real importance of such alterations.