Evaluation of infiltration of the superior mesenteric vein (SMV) and artery (SMA) fat planes has been considered in differentiating pancreatic carcinoma from pancreatitis. Some pancreatitis cases, however, can cause perivascular fat plane obliteration due to extension of the inflammatory process, mimicking appearances of carcinoma. This study investigated the diameters of SMV and SMA on CT scans, just caudal to the origin of SMA and portal confluens, in 68 pancreatitis and in 48 pancreatic carcinoma patients. SMA-to-SMV diameters (A/V diameter) were compared and ratios were obtained. In conclusion, it appears that when the A/V ratio is over 1.0, a malignant condition can be suspected. This may be used as a secondary criterion in the differential diagnosis of pancreatitis and pancreatic carcinoma.