Background: Variability in body mass index (BMI) (kg/m²) trajectories is associated with body composition and cardiometabolic markers in early childhood, but it is unknown how these associations track to later childhood. Objectives: We aimed to assess associations of BMI trajectories from 0 to 5 y with body composition and cardiometabolic markers at 10 y. Methods: In the Ethiopian infant anthropometry and body composition (iABC) birth cohort, we previously identified 4 distinct BMI trajectories from 0 to 5 y: stable low BMI (19.2%), normal BMI (48.8%), rapid growth to high BMI (17.9%), and slow growth to high BMI (14.1%). At 10 y, we obtained data from 320 children on anthropometry, body composition, abdominal subcutaneous and visceral fat, and cardiometabolic markers. Associations of BMI trajectories and 10-y outcomes were analyzed using multiple linear regression. Results: Compared with children with the normal BMI trajectory, those with rapid growth to high BMI had 1.7 cm (95% CI: 0.1, 3.3) larger waist circumference and those with slow growth to high had 0.63 kg/m² (95% CI: 0.09, 1.17) greater fat mass index and 0.19 cm (95% CI: 0.02, 0.37) greater abdominal subcutaneous fat, whereas those with stable low BMI had −0.28 kg/m² (95% CI: −0.59, 0.03) lower fat-free mass at 10 y. Although the confidence bands were wide and included the null value, children with rapid growth to high BMI trajectory had 48.6% (95% CI: −1.4, 123.8) higher C-peptide concentration and those with slow growth to high BMI had 29.8% (95% CI: −0.8, 69.8) higher insulin and 30.3% (95% CI: −1.1, 71.6) higher homeostasis model assessment of insulin resistance, whereas those with rapid growth to high BMI had −0.23 mmol/L (95% CI: −0.47, 0.02) lower total cholesterol concentration. The trajectories were not associated with abdominal visceral fat, blood pressure, glucose, and other lipids at 10 y. Conclusions: Children with rapid and slow growth to high BMI trajectories before 5 y tend to show higher measures of adiposity and higher concentrations of markers related to glucose metabolism at 10 y. Clinical Trial Registry: ISRCTN46718296 (https://www.isrctn.com/ISRCTN46718296).