Gastritis cystica profunda (GCP) is an uncommon hyperplastic benign lesion, and histologically characterized by hyperplasia and cystic dilatation of the gastric glands extending into the submucosal layer. GCP usually occurs at a gastroenterostomy site, although it can occasionally be found in an unoperated stomach. GCP is thought to be a possible precancerous lesion, since a few early gastric cancers associated with it were reported. Herein, we report a case of gastric adenoma associated with GCP in an unoperated patient. The sizes of both the GCP and adenoma overlying it have increased during a 10 year follow-up period. Adenoma on the latest biopsy showed low grade dysplasia, and it was successfully treated by endoscopic submucosal dissection.