WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: The risk of childhood obesity is influenced by a number of pre- and post-natal factors. The risk of childhood obesity is correlated with body weight during infancy, which might be related to the psychomotor development of the child. The previous literature on motor milestones and childhood overweight is limited and results are inconsistent. WHAT THIS STUDY ADDS: Weight status in early life and timing of achievement of gross motor milestones (the ability to sit and walk) are largely independent of each other. Timing of achievement of motor milestones in early life does not predict overweight or increased BMI later in childhood. BACKGROUND: Overweight may hinder achievement of gross motor milestones and delayed achievement of milestones may increase the risk of later overweight for reasons involving physical activity and the building of lean body mass. OBJECTIVE: To investigate whether increased birth weight and body mass index (BMI) at 5 months is associated with the achievement of the ability to sit up and walk and whether delayed achievement of these milestones is associated with overweight at age 7 years. METHODS: We used data from the Danish National Birth Cohort on 25 148 children born between 1998 and 2003. Follow-up took place from 2003 to 2010. Mean age at follow-up was 7.04 years. We used logistic and linear regression analyses. RESULTS: Birth weight and BMI at 5 months were marginally associated with earlier achievement of the ability to sit up and walk (regression coefficients between -0.027 months; [CI -0.042; -0.013] and -0.092 months [CI -0.118; -0.066]). Age in months of sitting and walking were not associated with overweight at age 7 years (ORs between 0.97 [CI 0.95-1.00] and 1.00 [CI 0.96-1.04]). Later achievement of sitting and walking predicted lower BMI at age 7 years (ln-BMI -z-scores between -0.023 [CI -0.029; -0.017] and -0.005 [CI -0.015; 0.005)). CONCLUSIONS: All observed associations were of negligible magnitude and we conclude that birth weight or BMI at age 5 months and motor milestones appear largely independent of each other and that timing of achievement of motor milestones seems not to be associated with later overweight or increased BMI.