The aim of this study was to estimate the social cost of the leptospirosis cases that were attributed to the natural disaster of January 2011 in Nova Friburgo (State of Rio de Janeiro, Brazil) through a partial economic assessment. This study utilized secondary data supplied by the Municipal Health Foundation of Nova Friburgo. Income scenarios based on the national and state minimum wages and on average income of the local population were employed. The total social cost of leptospirosis cases attributed to the 2011 disaster may range between US$21,500 and US$66,000 for the lower income scenario and between US$23,900 and US$100,800 for that of higher income. Empirical therapy represented a total avoided cost of US$14,800, in addition to a reduction in lethality. An estimated 31 deaths were avoided among confirmed cases of the disease, and no deaths resulted from the leptospirosis cases attributed to the natural disaster. There has been a significant post-disaster rise in leptospirosis incidence in the municipality, which illustrates the potential for increased cases--and hence costs--of this illness following natural disasters, which justifies the adoption of preventive measures in environmental health.