Leptospirosis is a re-emerging infectious disease that occurs in dogs in urban and rural environments. It is caused by a filamentous spiral bacterium that has a predilection for renal tubules. Acute renal failure, hepatic dysfunction, and hemorrhagic diathesis are the most common clinical signs. Treatment with antibiotics and supportive care can manage a high percentage of cases successfully. Newer vaccines developed in response to the change in frequency of certain serovars may decrease the incidence of clinical disease. Leptospirosis affects a wide variety of species and is zoonotic.