While the free fibular osteocutaneous flap is indispensable for mandibular reconstruction, reliable setting is often difficult because relative positions of the bone, skin island, and vascular pedicle are critical. We have an algorithm for donor-side selection of free fibular osteocutaneous flap. From July 2002 to March 2004, we performed 15 mandibular reconstructions using free fibular osteocutaneous flaps. We retrospectively classified these procedures as follows. In type I (flap harvested ipsilaterally to defect, n = 5), the skin island was fixed to the oral cavity, and the vascular pedicle emerged from the anterior aspect of the fibula. In type II (flap contralateral to defect, n = 5), the skin island was fixed to the oral cavity, and the vascular pedicle arose from the posterior aspect. In type III (flap contralateral to defect, n = 4), the skin island was fixed to the facial skin and the vascular pedicle arose from the anterior aspect. In type IV (flap ipsilateral to defect, n = 1), the skin island was fixed to the facial skin and the vascular pedicle arose from the posterior aspect. Flaps took completely except in 1 group II case with partial necrosis. Close attention to geometric characteristics of a free fibular osteocutaneous flap facilitates reconstruction of mandibular defects and selection of donor side.