BACKGROUND/AIMS: Anisakiasis is a well known parasitosis resulted from eating raw seafoods and there were many reports of cases. However, its endoscopic and clinical characteristics have not been reviewed well. The aim of this study was to clarify the gastric mucosal changes and influencing factors of upper gastrointestinal (UGI) anisakiasis. METHODS: We analyzed retrospectively the endoscopic and clinical characteristics of 141 cases with UGI anisakiasis diagnosed during UGI endoscopy, based on the review of medical records. The patients' data were collected consecutively from October 1999 through September 2006. RESULTS: In the 141 patients with UGI anisakiasis, the peak age was the 40s (44.7%). The female to male ratio was 1.82:1. The most prevailed season was winter (41.1%). The most frequent symptom was acute epigastric pain and 76.6% of the patients developed symptoms within 12 hours after the ingestion of raw seafoods. The greater curvature of body was the most preferred site of anisakid larvae. The median time from meal to symptom onset was shortest in esophageal location and longest in fundus location (3 vs. 18.7 hours). The various mucosal changes were observed and the most frequent mucosal change was edema (90.8%). Submucosal tumor was also found in 31.9% of the patients. The severity of mucosal change was related inversely with the time interval from meal to endoscopy (p=0.048). CONCLUSIONS: Anisakiasis presented various mucosal changes depending on the time interval from ingestion of raw seafood to endoscopy. Delayed endoscopy may lead chronic mucosal change and cause difficulty in the detection of anisakiasis. Therefore, the prompt endoscopic examination is required for the patients presenting acute gastrointestinal symptoms after taking raw fish.