Background: The anterolateral thigh (ALT) flap is a frequent choice for free flap transfer in head and neck cancer reconstruction because of its versatility. Preoperative mapping of the perforator pedicles of an ALT flap is still a challenge because of variations in vasculature. Although computed tomographic angiography (CTA) is used increasingly to evaluate the peripheral vasculature, the use of this method for evaluating the perforators of an ALT flap has not been described in detail. Methods: From September 2008 to March 2009, 32 patients underwent preoperative CTA before free ALT flap transfer for head and neck cancer reconstruction. The perforators were marked on a 64-section multidetector CT image for each patient. The preoperatively mapped perforators were compared with the actual intraoperative findings. Flap success rates and associated morbidity and complications were recorded. Results: Preoperative CTA identified major variations in perforators. Eighty-four were found by preoperative CTA; 64 of these were mapped to be explored during the operation, and 13 additional perforators were identified during surgery. The accuracy rate of identifying the branching origin of the ALT perforators was 98% (63/64). All of the ALT flaps survived except for one with necrosis (survival rate 97%). There was no donor site morbidity. Conclusions: Preoperative mapping of perforators by CTA proved valuable in free ALT flap transfer and shortened the operation time significantly. This modality provides useful information for head and neck cancer reconstruction in difficult cases, especially in patients with large or through-and-through defects that might need multiple perforators in flap design. © 2010 Elsevier Ltd. All rights reserved.