Abnormalities during two early developmental “windows” periods (intra-uterine [low birth weight and thinner size at birth] and early postnatal “catch-up” rapid weight gain, associated with fetal restriction) can be associated with increased risk for later life insulin resistance, metabolic syndrome and/or CV risk. It is not clear whether the critical period of rapid weight gain in relation to development of long-term cardiovascular and metabolic risks occurs during the first months of life, or in early childhood, or both. A continuous clustered metabolic risk score obtained by averaging standardized values for waist circumference, blood pressure, fasting triglycerides, HDL-cholesterol, glucose and insulin levels was used to examine the independent associations between weight gain during infancy (0-6 months) and early childhood (3-6 yr) with the components of the metabolic syndrome in 128 children of both sexes followed from birth to 17 yr. The results revealed that adjusted clustered metabolic risk at 17 yr was predicted by weight gain during infancy (P<0.0001) but not during early childhood (P=0.23). Therefore, very early interventions to moderate rapid weight gain may help to reduce cardiovascular risks in adults.