We tested whether normal-weight obesity might be associated with weight trajectories, body composition and metabolic traits.Body size trajectory since birth, body composition at age 20 years and metabolic traits were compared cross-sectionally among normal-weight Japanese women with low (<25.0%, n=67), normal (25.0-34.9%, n=160) and high (≥35.0 %, n=24) percentage body fat. Multivariate logistic regression analyses were used to identify most important determinants of normal-weight obesity (high percentage body fat).Fasting glucose averaged <84 mg/dL, homeostasis model assessment-insulin resistance <1.4 and triglyceride <70 mg/dL and did not differ among three groups. However, waist and trunk/leg fat ratio were higher, and weight-adjusted skeletal muscle mass was lower in normal-weight obesity. Serum and LDL cholesterol, apolipoprotein B (ApoB) and high-sensitivity C reactive protein were higher, and apolipoprotein A1 was lower in normal-weight obesity compared with the other two groups, whereas HDL cholesterol did not differ. Weight gain from birth to age 12 years was higher in normal-weight obesity. In multivariate logistic regression analyses, weight gain until 12 years (OR: 1.17,95% CI 1.02 to 1.34, p=0.02), ApoB (OR: 1.15, 95% CI 1.06 to 1.24, p<0.001) and weight-adjusted skeletal muscle mass (OR: 0.22, 95% CI 0.10 to 0.49, p<0.001) were associated with normal-weight obesity independently of trunk/leg fat ratio, high-sensitivity C reactive protein and apolipoprotein A1.Normal-weight obesity may be associated with early childhood growth, lower skeletal muscle mass and higher serum ApoB in young Japanese women through mechanisms unrelated to abdominal adiposity, inflammation and insulin resistance.© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.