An outbreak of human leptospirosis due to recreational activities occurred at São José dos Campos, São Paulo, Brazil in November 1987. It involved a group of persons who had participated in a gathering in a suburb club which had a swimming pool fed with natural water. Epidemiological investigation was carried out and laboratory tests from the patients were done. It was observed that a high prevalence of the pomona serotype (91%) was found in the serological analyses, while the presence of the agent of the infection could not be found in the water club swimming pool.