IntroductionWe report a case of severe leptospirosis that occurred during winter in Tokyo, the capital of Japan. Leptospirosis is endemic in tropical regions and extremely rare in the urban areas of Japan. Only six new cases were reported in Tokyo in 2014. Most leptospirosis cases reported in urban areas of Japan were a result of occupational hazards, and there is no previous report of leptospirosis in a homeless patient in Tokyo. We believe this report could provide a widened perspective about the clinical presentation and epidemiology of leptospirosis in Japan.Case presentationOur patient was a 73-year-old Asian man. He had been homeless for over 10 years, with exposure to rodents and their excrement in parks and on the streets. He presented with fever and severe inflammatory response, satisfying the diagnostic criteria for systemic inflammatory response syndrome. Laboratory findings showed multiple-organ dysfunction, including renal failure, liver failure with increased total bilirubin level, and coagulopathy with decreased platelets. We suspected leptospirosis on the basis of these clinical findings. The diagnosis was also confirmed by polymerase chain reaction first, and paired antibody titers on day 9, in the recovery period, showed positive results for three species.ConclusionsOur patient’s case suggests that even patients without a history of traveling abroad or exposure to freshwater can develop leptospirosis in winter in urban areas in Japan. If a patient has symptoms like fever, calf pain and MOF; as a differential diagnosis we should rule outthe Leptospirosis. From the perspective of sensitivity, specificity, and clinical convenience, polymerase chain reaction could be the preferred diagnostic tool of choice.