BACKGROUND Atopic dermatitis is a common inflammatory disease of the skin that usually begins in childhood and its diagnosis depends on clinical criteria. Recent reports have indicated that the worldwide prevalence of atopic dermatitis is increasing. The objective of this study was to determine the prevalence of atopic dermatitis in schoolchildren between the ages of six and seven in two school districts in Puerto Rico. METHODS The Laughter questionnaire, developed to determine the prevalence of atopic dermatitis in schoolchildren was translated and validated in Spanish. A population-based prevalence survey was conducted among second grade students in the districts of Guaynabo and Humacao, Puerto Rico. The prevalence of atopic dermatitis was determined by sex, school type (private or public), and geographical location (urban or rural) using the questionnaire. RESULTS Ninety-two percent (92 %) of the eligible schools participated in the study. A total of 2,393 questionnaires were distributed with a response rate of 53 %. The prevalence of atopic dermatitis among the population surveyed was 24.8%. The prevalence of atopic dermatitis by sex or geographic location was not significantly different (p>0.05). An excess of atopic dermatitis was observed in private schools (31.0%) when compared to public schools (19.9%). The effect remained after controlling potential confounders (POR Mantel-Haenszel = 1.37; 95%CI: 1.07 - 1.42). CONCLUSIONS This study presents evidence of a significant public health problem in Puerto Rico. The prevalence of atopic dermatitis in Puerto Rico is high and possibly a large percentage (70%) of the patients is not been diagnosed.