The endoscopic appearance of chronic hypertrophic pyloric gastropathy (CHPG) in five dogs is described. Several patterns of enlarged mucosal folds that surrounded and obstructed the pyloric canal were observed. Initially, endoscopically obtained biopsy samples of mucosa were judged to be histologi-cally normal. Diagnosis of CHPG was confirmed and relief of pyloric obstruction accomplished at exploratory laparotomy (in four dogs). Retrospective evaluation of pyloric tissue samples, obtained during endoscopy, identified subtle histological characteristics of CHPG. Gastric and duodenal neopla-sia or antral polyps can mimic the endoscopic appearance of CHPG but can be differentiated based on their endoscopic and histological appearance. These cases show that endoscopic examination is a valuable procedure for the diagnosis of CHPG in dogs that chronically vomit. (Journal of Veterinary Internal Medicine 1993; 7:335–341. Copyright © 1993 by the American College of Veterinary Internal Medicine.)