PubMed: 12090320 Leptospirosis is an infectious disease caused by pathogenic leptospires and is characterized by a broad spectrum of clinical manifestations, varying from inappearent infection to fulminant, fetal disease. Eighty-five to 90% of leptospirosis infections are self-limiting. However, 5-10% of infection by L.interrogans can cause renal tubular damage, microvascular injury, acute renal failure (ARF), and interstitial nephritis. We studied 36 patients with leptospirosis. Twenty-seven (65%) cases of 36 patients had ARF. Fourteen (51%) had nonoliguric ARF. In thirteen (48%) oliguria appeared on the third or fourth days of hospitalization. Serum BUN, creatinine, serum bilirubine, ALT, AST, potassium and thrombocytopenia levels were higher in oliguric than nonoliguric patients (p < 0.05). However, serum sodium, CPK levels were not different between oliguric and nonoliguric groups (p > 0.05). Thirteen patients (48%) needed in renal replacement therapy (RRT). 8 of them were treated by hemodialysis (HD) alone and 5 patients by HD in combination with hemoperfusion. Twenty-five patients (92%) recovered completely after 3-5 weeks. Two patients (7.4%) who had severe hepatorenal and hemorrhagic syndromes, died. We concluded that till now leptospirosis is actual problem for nephrologist in the developing countries because of very high percentage of renal disease, with good prognosis in patients without multiorgan failure and early treatment. Agricultural Research Foundation The diagnosis of ARF due to leptospirosis is supported by presence of high fever, intense muscle aching and jaundice. Renal involvement is frequent and hemodialysis is sometimes required. The pathogenesis of the tubular necrosis is unclear. Adequate therapy can prevent irreversible renal damage.