<b><i>Background/Aims:</i></b> Although early infant growth has implications for future health, body composition reference data in infancy are limited. The aim of this study was to describe reference data for fat mass (FM) and fat-free mass (FFM) corrected for length (L) within the first 3 months and to evaluate if these measures predict the body mass index (BMI) at 2 years. <b><i>Methods:</i></b> Term infants had air displacement plethysmography performed at birth (n = 1,063) and approximately 2 months later (n = 922, between 49 and 86 days). Age- and sex-specific reference data were generated for FM, FFM, FM/L³ and FFM/L² and compared with BMI at 2 years. <b><i>Results:</i></b> FM/L³ and FFM/L² were the optimal indices independent of length. In the first 3 months, mean FM/L³ increased (males, from 2.7 to 5.9 kg/m³; females, from 3.2 to 6.1 kg/m³), whereas FFM/L² remained relatively stable (males, from 11.8 to 12.7 kg/m²; females, from 12.8 to 12.1 kg/m²). The odds of a BMI Z-score ≥2 at 2 years increased with increasing FM (OR 2.7, 95% CI 1.97-3.7) and weight (OR 2.27, 95% CI 1.64-3.13) Z-scores at 2 months. <b><i>Conclusions:</i></b> FM/L³ and FFM/L² provide length-independent measures of FM and FFM in infancy. During the first 3 months, there is an increase in FM/L³, but not in FFM/L². The weight Z-score at 2 months is as good at predicting BMI at 2 years as body composition parameters.