This report discusses a case of leptospirosis in an 8 year old spayed female German Shepherd dog. The dog presented to her referring veterinarian in acute renal failure (BUN 147 mg/dL, creatinine 10.7 mg/dL) and was also Lyme positive on an in-house serology test. Referral to Cornell was for treatment of presumptive Lyme nephritis. At the time of referral, liver enzyme elevations had developed. Subsequent titers for leptospirosis were positive for serovar bratislava at 1:12,800. Treatment consisted of fluid diuresis, intravenous ampicillin, and doxycycline. Creatinine was twice normal (2.7 mg/dL) at discharge. Clinical aspects of leptospirosis as well as differentiation from Lyme nephritis and other causes of acute renal failure are discussed.