A 12-year-old spayed female Yorkshire Terrier with intermittent vomiting was diagnosed with regional granulomatous enteritis through histopathological examination. On ultrasonography and computed tomography, a focal thickened duodenal wall showed a mass-like appearance with indistinct wall layers. Marked uptake of (18)F-fluorodeoxyglucose was observed from the mass on positron emission tomography-computed tomography. Regional granulomatous enteritis is a rare form of inflammatory bowel disease and may have imaging features similar to intestinal tumors. This is the first study describing the diagnostic imaging features of ultrasonography, computed tomography and positron emission tomography-computed tomography for regional granulomatous enteritis in a dog.