DESIGN: We used cross-sectional data from the National Health and Morbidity Surveys 2006, 2011 and 2015. Individuals were classified into pre- (6-9 years), early (10-13 years) and mid- (14-17 years) adolescence. BMI status was determined according to the International Obesity Task Force (IOTF) and WHO criteria, using measured height and weight. We analysed trends using log-binomial regression, by sex-age groups, stratified by sociodemographic factors (ethnicity, residential area, household size and household income), and accounting for the complex survey design. Associations between sociodemographic factors and prevalence of thinness and overweight (obesity included) in 2015 were assessed using log-Poisson regression.

SETTING: Nationwide population-based surveys, Malaysia.

PARTICIPANTS: Eligible 6-17-year-olds from urban and rural residential areas (n 28 094).

RESULTS: The prevalence of thinness decreased from 2006 to 2015 (IOTF: boys from 22 % to 18 %, girls from 23 % to 19 %; WHO: boys from 9 % to 7 %, girls from 8 % to 6 %), while the prevalence of overweight increased (IOTF: boys from 20 % to 26 %, girls from 19 % to 24 %; WHO: boys from 25 % to 31 %, girls from 22 % to 27 %). These changes were statistically significant in most sex-age groups. Thinness and overweight co-existed in all sociodemographic subgroups, with variation in the prevalence estimates, but similar secular changes in most subgroups.