Using data from the Czech ELSPAC cohort (n = 5,151), this study applied latent growth mixture modelling to identify long-term BMI trajectories from childhood to adulthood and their parental determinants. Two trajectories were observed: normative and rising-risk. Higher maternal and paternal BMI increased the odds of rising-risk membership, while higher parental education reduced it. Sex-stratified analyses revealed a strong protective effect of maternal education in daughters only. The findings underscore the role of parental characteristics and child sex in shaping obesity risk across the life course.