The anterolateral thigh (ALT) flap was first described in 1984. It is now widely used in reconstructive surgery following extensive tumour resection in head and neck cancer. Routine preoperative perforator mapping is recommended due to variability of the vascular anatomy of the flap. A wide array of diagnostic tools is available for this purpose, including colour duplex sonography (CDS). In this study, we report our experience with CDS. The number, location, and course (myocutaneous or septocutaneous) of ALT perforators were assessed by CDS prior to reconstructive surgery in 22 patients with head and neck cancer. These data were compared with the intraoperative anatomical findings to assess agreement and reliability. The positive predictive value and sensitivity of CDS in detecting perforator location was 89.4 and 94.4%, respectively, when compared to the surgical report. CDS also identified the perforator course with 100% accuracy. Colour duplex sonography is an effective, non-invasive, and relatively inexpensive technique for assessing the location of skin perforators.