The utility of nitroglycerin is well established in coronary angiography but less so in other surgical fields. In this study, the authors investigated the utility of preoperative computed tomographic angiography after sublingual nitroglycerin followed by three-dimensional visualization for selecting suitable perforators in planning the free anterolateral thigh flap. The authors performed preoperative computed tomographic angiography following sublingual nitroglycerin (after screening for contraindications) in patients for whom reconstructive surgery with the free anterolateral thigh flap was planned. Data were reconstructed three-dimensionally, mapping location and course of source arteries and perforators. Suitable perforators were selected, and flap design was planned. The characteristics of perforators were analyzed statistically. Of 14 patients for whom surgery was planned, two had contraindications to nitroglycerin and underwent computed tomographic angiography alone. Nitroglycerin allowed for the visualization of more peripheral branches. The Hounsfield units at the deep fascia of perforators selected for surgery were significantly higher than for those not selected (p = 0.003). The distance from the intermuscular septum to the selected perforators was significantly shorter than the distance to nonselected perforators (p = 0.017). There were no adverse events, and all flaps survived. Sublingual nitroglycerin before computed tomographic angiography was safe and increased the visibility of perforators, enabling preoperative planning of flap design based on the three-dimensionally-reconstructed image. The authors highly recommend this procedure. CLINICAL QUESTION/LEVEL OF EVIDENCE:: Diagnostic, IV.