Canine sclerosing encapsulating peritonitis is a rarely reported condition. A 10-year-old male German shepherd dog cross was presented with a history of ascites, vomiting, soft faeces, anorexia and depression. Gathering of the intestinal loops in the middle portion of the abdomen was detected by radiography and ultrasonography. Cytological examination of Giemsa-stained smears from the popliteal lymph nodes revealed Leishmania species. The results of culture of serosanguineous fluid obtained by abdominocentesis were negative for bacteria and fungi. Laparotomy revealed a sac of fibrous tissue encasing most of the intestinal loops and numerous adhesions extending between them. Histologically, an uneven, diffusely thickened, visceral peritoneal membrane was found. A diagnosis of idiopathic sclerosing encapsulating peritonitis was made. The dog was euthanased because the intestinal wall was torn at many sites during dissection of the membrane.