Technical Abstract: Childhood obesity has been associated with delays in motor development using weight-for-length z-scores and subcutaneous fat. To study this further, percent body fat and motor development were assessed in children ages 3 to 24 months. Included were 455 children with a total of 1882 longitudinal observations. Standard anthropometric measures and dual-energy X-ray absorptiometry scans were used to evaluate growth and measure body fat mass. The motor scale of the Bayley Scales of Infant Development II was used to assess motor development at 3, 6, 9, 12 and 24 months. Overweight children were significantly more likely to have a lower motor development score at a subsequent assessment compared to lean children (P=0.01). Additionally, children with higher fat mass were significantly more likely to have lower motor scores at the time of the body composition measures as well as at a subsequent assessment of motor development (P=0.02 and P=0.03, respectively). These data confirm that overweight children have statistically lower motor development scores. Despite the statistical significance of these results, absolute differences in motor scores between lean and overweight children were very small (0.7 at 3 mo, 1.9 at 6 mo, 2.0 at 9 mo, 0.4 at 12 mo, 4.5 at 24 mo), and thus the clinical significance and level of concern during the first 2 years of life may be negligible.