Information about Mycoplasma pneumoniae infections in tropical countries is scarce. This study reports the prevalence of anti-M. pneumoniae antibodies among schoolchildren from the tropical community of Palmares, Costa Rica. The serum samples were collected in July 1983 from 2021 children who represented 99% of the county's schoolchildren. Immunofluorescence (IFA) and in some cases ELISA serological methods were applied. IFA seropositivity was high (53%) and ranged from 22% to 79% depending on the district. Marked differences in the prevalence of antibodies in children attending schools of neighboring communities, suggest that the school may be epidemiologically important as a focus to spread mycoplasma infections among children. The presence of a low percentage of antibodies (IgG, IgM and IgA) against the 168 kd- M. pneumoniae antigen suggested that there were few cases of active or recent infections.