The lower trapezius island musculocutaneous flap is valuable in head and neck reconstruction. It offers thin, pliable tissue and a long arc of rotation to reach virtually any defect in the head and neck. Recent reports have shown unacceptably high rates of failure and have questioned the reliability of the vascularity. We report our experience with 45 reconstructions using the lower trapezius island musculocutaneous flap. The literature is reviewed and the vascular anatomy is described in detail. The concept of angiosomes is applied to the trapezius muscle to help explain the reasons for flap failure and to provide guidelines for flap design and harvest.