This case report describes a 68-year-old man who presented with bronchiolitis obliterans organizing pneumonia (BOOP) and gastric carcinoma. During evaluation, including a colonoscopy, he was found to have distal colitis and a giant polypoid lesion in the cecum that was diagnosed as localized giant inflammatory polyposis (LGIP) by magnifying colonoscopy. The patient was treated over a period of 3 years without surgery, and the LGIP was reduced in size during the follow-up period. Magnifying observation was useful to distinguish LGIP from a neoplastic lesion.