Abstract: In this study, researchers present 3 cases of dogs with chronic diarrheas where errors were committed in the diagnostic process that had fatal consequences for patients. These mistakes included: veterinarians took a long time to perform biopsies take biopsies of only certain portions of the gastrointestinal tract in dogs with weight loss and hipoproteinemia and practice a digestive endoscopy without take biopsies because presenting a normal endoscopic image. Finally, researchers describe guidelines for diagnosis of chronic diarrheas and to take gastrointestinal biopsies.