Contrast enhancement resulting from surgical trauma may mimic residual enhancing tumor, thereby complicating the interpretation of postoperative computed tomographic scans. We assessed the natural history of postoperative enhancement in 10 patients with brain tumor. Contrast enhancement distinguishable from residual enhancing tumor appeared along the operative margin following tumor resections but not lobectomies. Enhancement appeared as early as the fifth postoperative day, was most intense at two weeks, and persisted for several months. Prior to the fifth postoperative day, enhancement reflected residual tumor. Edema and artifacts were more prominent on the first and second postoperative days than on the third and fourth. We recommend that postoperative computed tomographic scans to assess residual enhancing tumor be performed on the third or fourth postoperative day. This timing avoids postoperative enhancement and minimizes interpretative difficulties caused by artifacts.