Cutaneous vascular anatomy of the flank and the hip was studied in the rat. Investigation was done by anatomical dissection, ink injection to the axial artery and flap harvesting in living rats. Anatomical dissection and India ink injection revealed that the rat's flank and hip skin derives its blood supply from the iliac branch of the iliolumbar artery, which originates from the lateral aspect of the abdominal aorta. The vascular territory of the iliac branch of the iliolumbar artery was defined as follows: the medial border--along the midline of the back from the 12th rib to the proximal part of the tail; the lateral border-anterior axillary line corresponding with the length of the medial border; the cephalic border--a line joining the medial and lateral border at the level of the 12th rib; and the caudal border--the posterior lateral line of the hip. On the basis of the vascular territory demarcated by India ink injection, bilateral vascular pedicle island cutaneous flaps were harvested in living rats. Results showed total survival of all flaps. This flap is easily made, and it could be used as a reliable model for flap research.