Purpose: To determine usefulness of spiral CT in the preoperative evaluation of peritoneal seeding from a gastric carcinoma. Materials and Methods: From a database of 411 consecutive patients with surgically proven advanced gastric carcinoma obtained over a six-month period, 17 with peritoneal seeding and a control group of 24 without peritoneal seeding underwent spiral CT scanning with 7-8 mm scan thickness and interval during the portal phase. Preoperative CT images were analyzed by two readers who reached a consensus with regard to the presence and location of the ascites, thickening of the parietal peritoneum, and changes in the omentum and mesentery. Results: Ascites was present in 47%) (8/17) of patients with peritoneal seeding The right subhepatic space (n = 6,35%) and right paracolic gutter (n = 5,29%)-but not the cul-de-sac (n = 2, 12%)-were common sites of fluid collection. Permeative changes in the omentum and mesentery were seen in 187o (3/17) and 127o (2/17) of patients, respectively. Among five controls with false positive results, ascites in the cut-de-sac was present in three (two males and one female, 12%) while omental nodules and a thickened peritoneum were found in two (8%) and one (4%) , respectively. In nine controls with false negative results, small disseminated nodules were seen in the mesentery and omentum at surgical field. The sensitivity and specificity of spiral CT were 47% (8/17) and 79% (19/24), respectively. Conclusion: In terms of sensitivity and specificity, spiral CT is not especially accurate in distinguishing peritoneal seeding from gastric carcinoma.