OBJECTIVE A retrospective study was performed to determine the causes of false-positive diagnoses based on CT findings obtained during superior mesenteric arterial portography (CT portography) and to correlate the imaging characteristics of the incorrectly diagnosed lesions with their pathologic findings. METHODS In a series of 52 patients who had CT portography before surgical exploration of the liver, eight had a total of 10 false-positive findings, yielding a false-positive diagnosis rate of 15%. In eight cases, the false-positive findings from CT portography were correlated with the histologic material obtained during partial hepatic resection or intraoperative biopsies at the corresponding sites. RESULTS Of the 10 false-positive findings on CT portograms, seven led to false-positive diagnoses of hepatic tumors. Conversely, three nontumorous false-positive findings were erroneously considered to be portal perfusion defects. The final diagnoses based on pathologic findings included focal fatty infiltration of the liver (three), cirrhosis (two), and portal perfusion defect (three). Two false-positive findings for which no histologic correlation was possible were considered to be portal perfusion defects on the basis of intraoperative findings. CONCLUSIONS Recognition of false-positive findings is crucial in the preoperative evaluation of hepatic tumors because the findings may be interpreted as contraindications for surgery in patients who have operable tumors. The pathologic correlations show that several different entities can cause diagnoses based on CT portographic findings to be false-positive. However, differentiating between those entities remains a diagnostic challenge.