PURPOSE: To assess the malignant potential of small(< or =15mm) portal defects seen on CT arterial portography,the findings of CT hepatic arteriography and lipiodol CT CT were reviewed. MATERIALS AND METHODS: In 91 patientswho underwent both CTAP and CTHA, small portal defects were re-viewed for frequency, multiplicity and location. Weprospectively evauluated changes in the size and enhance-ment pattern of malignant lesions on follow up CTaccording to density on CTHA, location, lipiodol deposits on lipiodol CT, and multiplicity. RESULTS: Among the 91patients, 102 small defects were defected in 42 patients(46%). Small portal defects were benign, malignant, and ofundetermined malignant potential in 77%, 20% and 3% of cases, respectively. Small portal defects that werehyperattenuated on CTHA, and lipiodol deposits on lipiodol CT, were malignant in 42% and 70% of cases,respectively. Location and multiplicity did not show statistically significant variation between benign andmalignant defects. CONCLUSION: Small portal defects are common and there is a high probability that portaldefects smaller than 15mm are benign, even in patients with a known hepatic mass and defect that washyperattenuated on CTHA. If a small defect showed lipiodol deposit on lipiodol CT, malignancy must be suspected.