Hiatal hernia is a disorder consisting in the dislocation of the abdominal part of the esophagus and/or part of the stomach into the chest cavity, through esophageal hiatus. It can be of congenital or acquired character. Two types of hiatal hernia, slide-in or periesophageal, have been classified in dogs and cats. The objective of this study was to present the authors’ experiences with endoscopic diagnostics of slide-in hiatal hernia in dogs based on clinical cases. The described clinical cases indicate the high usefulness of the endoscopic examination in the diagnosis of slide-in hiatal hernia. Moreover, this examination allows for the evaluation of the degree of progression of esophagus mucosa lesions that result from gastro-esophageal reflux.