Abstract A 2-year-old male Maremma sheepdog presenting with chronic vomiting-regurgitation was examined at the University Veterinary Teaching Hospital, Camerino University. An oesophagogastroscopy with a single blue + green (BG) filter restricting wavelengths from 400 to 550 nm was carried out. A conventional white light endoscopy showed a dilated oesophagus with mildly diffuse erythematous mucosa (more accentuated proximal to the cardia); some portions of the gastric mucosa were covered with fluids and appeared only slightly erythematous. A blue green endoscopy highlighted the oesophageal lesions in dark blue, which made them appear more clearly defined from the remaining mucosa. In the gastric antrum, a small, slightly darker blue roundish area was visible. This area did not show up under the white light endoscopy. A histopathological assessment of biopsy specimens from the distal oesophagus, antrum (including the area highlighted only by BG endoscopy) and gastric body showed chronic-active hyperplastic esophagitis and superficial squamous epithelial dysplasia, while gastric samples showed severe diffuse hyperaemic gastritis of the antrum and superficial diffuse atrophy of the gastric body. The authors believe that the use of a BG endoscopy could be useful in veterinary medicine to increase the diagnostic potential of endoscopic assessment in animals.