This study evaluated all children born in 1993 in hospitals from Pelotas, Rio Grande do Sul, Brazil. Besides a perinatal study, a sample of 20% (1400 children) was followed through home visits during the first year. During these visits the nutritional status was assessed and a screening test for development (Denver II Test) was performed. Thirty-four per cent of the children assessed at 12 months failed this screening. Failure was associated with socioeconomic status, with low-income children presenting twice the risk of those from more affluent families (p<0,001). Failure in the screening test was also associated with birthweight, and children weighing less than 2,500 g showed three times the risk of those with a birthweight equal to or greater than 2,500 g (p<0,001). In addition, children weighing less than 2000 g at birth were at three times the risk of failing the test as compared to those weighing between 2000g and 2499g. Results suggest that birthweight and family income are strongly related to the potential risk of developmental delays at the age of 12 months. It also points to the need for systematic developmental screening and early intervention programs in children at risk.