In this retrospective study, the medical records of 23 dogs with the sonographic feature of small intestinal hyperechoic mucosal striations and an endoscopic or surgical intestinal biopsy were reviewed. Histopathologic lacteal dilation was present in 96% of dogs with mucosal striations. Sonographic findings associated with mucosal striations included: mild jejunal wall thickening (96%), mild duodenal wall thickening (78%), mucosal speckles (70%), and abdominal effusion (87%). The mucosal striations were diffuse (70%) or multifocal (30%) and did not cause loss of wall layering, except in one dog with a severe mural lipogranuloma. Mesenteric lymphadenopathy was identified in 9% of dogs. Thirteen dogs with endoscopic biopsies had mild to moderate villus lacteal dilation and the nine dogs with surgical biopsies had moderate to severe dilation. Inflammatory infiltrates were mild (61%) or moderate (30%) with variable numbers and combinations of cells, including eosinophils (65%), plasma cells (61%), lymphocytes (57%), and neutrophils (30%); one dog had disseminated villus histiocytic sarcoma. The biochemistry changes and clinical signs were consistent with protein-losing enteropathy in 78% of dogs. Hyperechoic mucosal striations in dogs are associated with lacteal dilation and are frequently associated with mucosal inflammation and protein losing enteropathy.