OBJECTIVE The objective was to study the effects of repeated antenatal corticosteroids on birth size, growth, and development in preterm infants. STUDY DESIGN This observational study followed up for 3 years a prospective geographic cohort in the state of Western Australia of 477 singleton infants born at <33 weeks' gestation. RESULTS Birth weight ratio decreased with increasing number of corticosteroid courses (P =.001), and multivariate analyses confirmed a reduction in birth weight of as much as 9% (P =.014) and a reduction in head circumference of as much as 4% (P =.0024). There were no additional benefits in mortality or respiratory outcomes, and there was a trend toward more severe chronic lung disease. At age 3 years growth and severe disability outcomes did not appear to be related to increasing number of corticosteroid courses. CONCLUSIONS In this cohort study repeated corticosteroid courses were associated with adverse effects on size at birth without apparent benefits. These changes have the potential to affect later development.