1. In a large, population representative,Chinese birth cohort, higher birth weight and rapid growth, particularly at 0-3 months, were associated with higher body mass index (BMI) at 7 years. 2. Boys born heavy who had grown fast had the highest BMI, but rapid growth had the largest impact in lighter-born boys. 3. Rapid growth at 0-3 months or 3-12 months was not associated with a compensatory lower risk of serious infectious morbidity. 4. The ability to grow fast may be an embodiment of good health status, rather than fast growth being causally protective.