Computed tomographic (CT) brain scans were performed without and with contrast enhancement within 24 h of craniotomy in 26 patients undergoing 27 operations. Postoperative scans were retrospectively reviewed for evidence of contrast enhancement, the pattern of enhancement and the presence of blood on the postoperative scans. Contrast enhancement was seen in the resection bed in 33% of patients undergoing gross total resection of their lesions, and was absent in 50% of patients with known residual disease. Enhancement along a corticotomy was present in 18% and distant meningeal enhancement was identified in 19% of patients. These enhancement rates were unrelated to steroid dosages, duration of surgery, or the interval between operation and scanning. It was not possible to delineate residual tumor in 63% of the patients, due to a postoperative enhancement pattern that stimulated enhancing vessels, the presence of hemorrhage, or due to the absence of calcification or preoperative enhancement. None of the scans were affected by technical problems (motion artifact, inability to complete the scan) potentially associated with scanning within 24 h of craniotomy. Small amounts of residual tumor remain undetectable, particularly due to hemorrhage in the resection bed. Although no distinct advantage in defining residual disease was obtained compared to scanning at 72 h, the overall rate of findings not related to neoplasm was slightly less for scans obtained within 24 h.