The free anterolateral thigh flap is becoming one of the most preferred options for soft-tissue defect reconstruction. Between June of 1996 and August of 2000, 672 anterolateral thigh flaps were used in 660 patients in Chang Gung Memorial Hospital. A total of 439 flaps were cutaneous or fasciocutaneous flaps based on musculocutaneous perforators. The analysis of the flap failures was done only in this perforator series. In six cases, no suitable skin vessel was found during the dissection of the flaps. The complete success rate was 96.58 percent (424 of 439). Of the 15 failure cases, eight were complete and seven were partial (10 percent to 60 percent of the flap). Thirty-four flaps were reexplored, and 19 (56 percent) were salvaged. In this study, some of the reasons for the flap failure, unique to the anterolateral thigh perforator flap, were identified. They include inadvertent division of perforator at the fascial plane as a result of inadequate knowledge of perforator anatomy, inadvertent injury to the perforator during intramuscular dissection (noted by the surgeon or ignored) as a result of inexperience, and twisting of the pedicle during inset of the flap at the recipient site. Technical pearls in the harvest of the anterolateral thigh perforator flap are as follows: mapping of the skin vessels with a Doppler probe before flap design, meticulous dissection of the perforator under surgical loupe or even lower-magnification microscope, inclusion of a small fascia cuff around the perforator, and intermittent topical use of Xylocaine during the intramuscular dissection of the perforators. During reexploration, one must search for twisting of the pedicle and small bleeders from the branches of the intramuscular perforators.