BACKGROUND: While higher smoking prevalences have been better described for adults and adolescents in the mountainous areas than in the plain area in Taiwan, no studies have previously examined whether this disparity begins with children in elementary schools. The purpose of this study was thus designed to explore clustering in smoking behavior among elementary school children attending mountain schools compared to those attending city schools. METHODS: This study analyzed data obtained by a survey on smoking behavior collected during the School Smoking Survey Project performed in 13 elementary schools of Taoyuan County, Taiwan. Overall, 1585 third and fourth graders (mean age 8.9 years) participated in the study. A multilevel logistic regression analysis was performed to explore the effects of school location on individual smoking behavior among elementary school children while controlling for individual-level characteristics. RESULTS: Overall, 34.9% of the elementary school students in the mountain schools reported having tried cigarette smoking compared to only 9.6% of students from city schools. Students attending mountain schools had a greater likelihood of reporting smoking than students attending city schools after controlling for individual-level characteristics (OR = 2.57, 95% CI = 1.10-5.99). CONCLUSIONS: A significant individual clustering in smoking behavior was found among third- and fourth-grade children attending mountain schools. The new findings suggest that the adult geographic smoking disparity begins in elementary school. Interventions aimed at reducing smoking disparity in adults need to target elementary schools in high-risk locations. ? 2009, American School Health Association.