Human leptospirosis is a subject of increasing interest. Although this disease was frequently associated with individuals whose occupation or geographic location placed them in close proximity to wild animals or farm animals, recent cases have been particularly prevalent in young children and adolescents in urban and suburban America. Many of the recent cases have been acquired from household pets, particularly from dogs or hamsters. In particular, healthy dogs who have been immunized with leptospiral organisms, thereby creating a significant risk for their owners. This article will review the pathophysiology, clincal manifestations, laboratory diagnosis, treatment, and prevention of leptospirosis in the modern era, with particular emphasis on a more complete understanding of the epidemiology of this disorder.