Background: Growth patterns of breastfed and formula-fed infants may differ, with formula-fed infants growing more rapidly than breastfed infants into childhood and adulthood. Objective: Our objectives were to identify growth patterns and investigate early nutritional programming potential on growth patterns at 6 y and on body composition at 20 y. Design: TheWest Australian Pregnancy Cohort (Raine) Study and 3 European cohort studies (European Childhood Obesity Trial, Norwegian Human Milk Study, and Prevention of Coeliac Disease) that collaborate in the European Union-funded Early Nutrition project combined, harmonized, and pooled data on full breastfeeding, anthropometry, and body composition. Latent growth mixture modeling was applied to identify growth patterns among the 6708 individual growth trajectories. The association of full breastfeeding for <3 mo compared with ≥3 mo with the identified trajectory classes was assessed by logistic regression. Differences in body composition at 20 y among the identified trajectory classes were tested by analysis of variance. Results: Three body mass index (BMI; in kg/m2) trajectory patterns were identified and labeled as follows-class 1: Persistent, accelerating, rapid growth (5%); class 2: Early, nonpersistent, rapid growth (40%); and class 3: normative growth (55%). A shorter duration of full breastfeeding for <3 mo was associated with being in rapidgrowth class 1 (OR: 2.66; 95% CI: 1.48, 4.79) and class 2 (OR: 1.96; 95% CI: 1.51, 2.55) rather than the normative-growth class 3 after adjustment for covariates. Both rapid-growth classes showed significant associations with body composition at 20 y (P <0.0001). Conclusions: Full breastfeeding for <3 mo compared with ≥3 mo may be associated with rapid growth in early childhood and body composition in young adulthood. Rapid-growth patterns in early childhood could be a mediating link between infant feeding and long-term obesity risk.