Leptospirosis is an acute febrile disease with varied manifestations characterized by vasculitis. The severity of disease ranges from asymptomatic or subclinical to self-limited systemic illness (approximately 90% of patients) to life-threatening illness with jaundice, renal failure, and hemorrhagic pneumonitis. The clinical presentation typically is biphasic, with an acute septicemia phase usually lasting 1 week, which is followed by a second immune-mediated phase. Regardless of its severity, the acute phase is characterized by nonspecific symptoms, including fever, chills, headache, nausea, vomiting, and a transient rash. The most distinct clinical findings are conjunctival suffusion without purulent discharge (30%-99% of cases) and myalgias of the calf and lumbar regions (40% to 100% of cases). In some patients, the 2 phases are separated by a short-lived abatement of fever (3-4 days). Findings commonly associated with the immune-mediated phase include fever, aseptic meningitis, conjunctival suffusion, uveitis, muscle tenderness, adenopathy, and purpuric rash. Approximately 10% of patients have severe illness, including jaundice and renal dysfunction (Weil syndrome), hemorrhagic pneumonitis, cardiac arrhythmias, or circulatory collapse associated with a case-fatality rate of 5% to 15%. The overall duration of symptoms for both phases of disease varies from less than 1 week to several months. Asymptomatic or subclinical infection is frequent, and seroconversion can occur, especially in settings of endemic infection.