Objectives: Identify the frequency and risk factors of leptospirosis outbreak in the locality of residence of an index case with icterohemorrhagic syndrome. Material and methods: Were interviewed and examined children and teenagers from residence area of index case who frequented a common source of infection between January and February, 2004. All of them were screened for leptospirosis using IgM-ELISA and microscopic agglutination test (MAT), PCR and culture. Results: Were enrolled 77 subjects between 2 to 18 years old, only 21 (27.3%) were confirmed cases. The signs and symptoms of the confirmed cases were fever, headache, myalgia, abdominal pain, nausea, vomiting and anorexia. Three of them presented with jaundice, bleeding and renal failure. The presence of contact with the source of infection of underground water (OR=3.26, 95%IC 1.22 to 8.72), and the contact with dogs in the water source of infection (OR = 5.63, 95%IC = 1.40 to 22.63) were identified as significant factors associated with leptospirosis. Conclusions: It was confirmed an outbreak of leptospirosis in a new epidemiological context related to a common source of underground water and associated by contact with dogs in the same source. This data will allow to expand the knowledge about this disease as well as to consider leptospirosis as an important cause of acute febrile disease.