Without well recognizing the vascular territories of the perforator, surgery might damage the pedicle and diminish flap survival. This study described a transillumination method for intraoperative mapping of the subfascial plexus of the perforator in the head and neck reconstruction with an anterolateral thigh (ALT) flap and also compared the perioperative outcomes and complications of the method with those of the conventional two-pedicle ALT flap. Between January 2011 and December 2017, 26 patients who underwent head and neck reconstruction with ALT flaps were evaluated as follows: 13 underwent the transillumination method (case group), and 13 (age- and sex-matched) underwent standard two-pedicle flap procedures (control group). Demographic factors, diagnosis, flap size, recipient site, perioperative data, and postoperative complications were compared between the two groups. There was no significant difference in age, sex, diagnosis, recipient sites, and flap size between the case and control groups. Regarding the perioperative outcomes, the harvesting time was significantly shorter in the case group than in the control group (60 vs. 100 minutes, p < 0.001). The operative time was shorter in the case group than in the control group, but this difference was not statistically significant (300 vs. 420 minutes, p = 0.058). The transillumination method can allow plastic surgeons to easily identify the perforator vascular plexus of the ALT flap, which facilitates intraoperative flap design in head and neck reconstruction.