Leptospirosis is an infectious disease caused by pathogenic leptospires and may vary in degree from an asymptomatic infection to severe and fatal illness. Sixteen patients (all males; aged 40+/-17 years) with leptospirosis were admitted to Sişli Etfal Training and Research Hospital between July 1998 and August 2003 and were retrospectively reviewed. Age, gender, occupation, clinical presentation, laboratory features, seasonal distribution of the disease, diagnostical approach, and prognostic factors were evaluated. Eleven patients were cured with no complication; four patients died of hepatic and/or renal failure. Eight patients presented with acute renal failure; seven of them needed dialytic support. One patient developed chronic renal failure and had to undergo regular hemodialysis. All deceased patients (aged 61+/-7 years) were anuric at admission and their serum bilirubin changed between 39-44 mg/dL (mean 41.3+/-2.2 mg/dL). Cured patients ranged in age from 14-62 years (34+/-14 years) and their serum bilirubin levels ranged from 9-35 mg/dL (23.1+/-11.4 mg/dL). Crystalline penicillin G 12 million U/day was administered to all patients. Six patients also received hepatic coma treatment. This study emphasizes that leptospirosis presenting with renal failure is a severe disease, and mortality is frequently related to delays in diagnosis due to lack of clinical understanding. The association of acute renal failure and jaundice should lead the clinician to suspect leptospirosis. We concluded that old age, oliguria/anuria, high serum bilirubin levels (>36 mg/dL), and high serum potassium levels might be risk factors that increase mortality in leptospirosis.