The supplementary motor area (SMA) is a region located within each cerebral hemisphere at the posterior mesial border of the frontal lobe adjacent to the falx. The functional significance of this area has been somewhat unclear, and information regarding its influence on motor output has largely been based on evoked responses to direct stimulation in primates and humans. In this series of patients with primary and metastatic tumors involving the dominant hemisphere SMA, a distinct pattern of postoperative deficits and recovery has emerged which emphasizes the role of this critical area in the initiation of motor activity, including speech. Based upon this analysis, ablation of this region after first identifying the primary motor cortex may be accomplished without risk of permanent loss of motor activity or speech function, despite the initial severe deficits.