Perianal fistulas are a chronic, debilitating disease that requires lifelong monitoring and, potentially, lifelong treatment. Lesions are characterized by ulcerations with draining fistulous tracts around the anal region. Most dogs experience significant pain and discomfort with this condition. Bacterial infections are a frequent secondary problem. Definitive diagnosis is based on clinical signs, signalment, history, and a thorough examination. The most successful treatment is immunomodulatory therapy (cyclosporine with or without ketoconazole and topical tacrolimus). Perianal fistulas can be difficult to treat, frustrating both veterinarians and owners.