Two cohorts of children born in the city of Pelotas, Southern Brazil, in 1993 and 2004, were compared in terms of neuro-psychomotor development at the age of 12 months. Children were evaluated using the Denver II screening test. Analyses were performed using the Poisson regression technique. The prevalence of suspected developmental delay fell from 37,1% in 1993 to 21.4% in 2004 and was inversely proportional to family income and birth weight. Among children born weighing under 2,000 g, there was a fourfold reduction in the prevalence of developmental delay between 1993 and 2004. With regard to family income, the poorest group showed the greatest reduction between the two cohorts - a 30% reduction in risk. Our results confirm the influence of income and birth weight on child development. The decrease in the prevalence of developmental delay in the last decade reflects, among other factors, improvements in neonatal care, increased coverage of developmental monitoring in the first year of life, and longer breastfeeding duration. Despite this reduction, the prevalence of developmental delay is still high, reinforcing the need for early diagnosis and intervention.