We reviewed the laboratory-confirmed cases of leptospirosis in Ramathibodi Hospital, a medical-school hospital in Bangkok, to assess the documented cases of leptospirosis in Bangkok and the medical complications of severe cases. There were 59 cases from January 1994 to December 2000. More than half of the cases were Bangkok residents and did not travel outside Bangkok in the preceding 2 weeks. The majority of the cases presented in late rainy season. The clinical presentation, laboratory findings, medical complication, treatment and outcome are given. Leptospirosis in the urban area is common and should be recognized, particularly in rainy season.