Objective Investigate the prevalence and epidemiological characteristics of flatfoot among a sample of adolescents(grade 3,5 and 7)in the Northeastern Chongqing,analyze the influencing factors,to provide a scientific basis for selecting intervention strategies.Methods Utilizing plantar optical observation mirrors and questionnaires,a flatfoot screening was conducted among grade 3,5 and 7 school-aged adolescents from 10 urban and rural schools in Wanzhou District,Chongqing.Relevant parameters were recorded,and uni-variate logistic regression analysis was performed considering gender,genetics,BMI,exercise duration,foot-wear,history of ankle trauma,awareness of risks,medical consultation history,and knowledge of preventive measures for flatfoot prevalence.Variables with statistically significant differences in the univariate logistic a-nalysis were included in the multivariate logistic regression analysis.Results In a sample of 5 058 school-age adolescents,2 163 were diagnosed with flatfoot,yielding a prevalence rate of 42.76%(2 163/5 058).Urban and rural areas difference:urban areas had a rate of 43.70%(1 444/3 304),while rural areas had a rate of 40.99%(719/1 754),no statistically significant difference was found between the two(χ2=3.334,P=0.068).Gender difference:males had a rate of 45.56%(1 212/2 660),and females had a rate of 39.66%(951/2 398),the prev-alence rate was higher in males than in females,with a statistically significant difference(χ2=17.730,P<0.001).Grade difference:the prevalence rate in grade 3 was 49.45%(822/1 662),in grade 5 was 42.78%(727/1 699),and in grade 7 was 36.18%(614/1 697),there was a statistically significant among different grades(χ2=60.473,P<0.001),while the prevalence rate in grade 3 was significantly higher than that in grade 5 and 7,and it showed a decreasing trend with the increase of the students'grade level(χ2 trend=24.223,P<0.001).Genetic differences:the proportion of individuals with a positive genetic predisposition to flat feet was 15.53%(336/2 163),the influence of genetics on the occurrence of flat feet was statistically significant(χ2=70.232,P<0.001);furthermore,there was a higher genetic tendency towards severe flatfoot,with statistically significant difference(χ2trend=44.976,P<0.001).BMI difference:comparison of flatfoot severity across differ-ent BMI strata showed a significant difference(χ2trend=21.118,P=0.002),indicating that varying BMI levels affect the prevalence of flatfoot.Multivariate logistic regression analysis showed that gender,genetics,and BMI(18.5-<25.0 kg/m2)were the influencing factors of flatfoot among adolescents in Northeastern Chongqing(P<0.05).Conclusion The incidence of flatfoot among school-age adolescents decreases with in-creasing grade,with lower rates among girls than boys,and there is a genetic predisposition.Most flatfoot are mild,and BMI is a high-risk factor.Early intervention should be implemented for flatfoot in adolescents.