The objective of this study was to determine the prevalence of flexible flatfoot in elementary school children in Taiwan and evaluate the relationship between flatfoot and obesity, gender, and age. A sample of 2,083 children, between 7 and 12 years of age from public elementary schools in northern Taiwan was analyzed. Children were stratified into groups according to age: 7, 8, 9, 10, 11, or 12 years old. Demographic information was obtained, and the presence of flatfoot determined by footprint analysis and grading according to Denis flatfoot staging. A total of 1,222 (59%) children were documented with flatfoot. The incidence percentages of flatfoot were: 67% of males, 49% of females, and 75%, 65%, 57%, and 48% of obese, overweight, normal weight, and underweight children, respectively. A preponderance of flatfoot was observed among 8-year-olds. Multivariate analyses indicated that 8- and 9-year-olds were 1.52 and 0.72 times more likely to have flatfoot than 7-year-olds. Males were twice as likely to have flatfoot as females. Children who were obese or overweight were 2.66 and 1.39 times more likely to have flatfoot than those of average weight. The results of this study indicate that the prevalence of flexible flatfoot is highest among males who are obese and overweight, particularly in the age range of 7 to 8 years.