Leptospirosis is a worldwide zoonosis, that is most frequently encountered in tropical and subtropical areas. In France, during the last years, its incidence has increased. Epidemiology is conditioned by a wide animal reservoir. Important clinical polymorphism makes diagnosis difficult. Laboratory abnormalities such as increased serum C-reactive protein and triglycerides and suggestive. Early diagnosis is now possible by using polymerase chain reaction methods. Early treatment with an aminopenicillin can improve prognosis which remains poor, especially in case of renal or pulmonary involvement. Pathophysiology of the disease still needs to be thoroughly studied.