Objective: Antenatal corticosteroids are extensively given in pregnancies with threatened preterm labour as a prophylactic method to reduce some kinds of neonatal diseases. Dexamethasone is one kind of commonly used corticosteroid, but controversies still remain whether it leads to adverse effects on neonatal long-term development or not. The purpose of this study was to investigate the influence of prenatal exposure to one or two dosages of dexamethasone on neonatal physical and cognitive development of children at 1, 3 and 6 years of age. Methods: This was a retrospective cohort study. The body length, head circumference and body weight were measured in every infant and child to evaluate physical development. The mental development index (MDI) and a psychomotor development index (PDI) were used to evaluate mental and cognitive development in children of ages 1 year and 3 years while verbal intelligence quotient (VIQ) and performance intelligence quotient (PIQ) scores were used to evaluate mental and cognitive development in children of age of 6 years. There were 1554 infants at 1 year, 1328 children at 3 years and 1297 preschool children at 6 years followed. Results: There were no significant differences between antenatal dexamethasone exposure groups and antenatal dexamethasone non-exposure groups on physical development index and MDI, PDI, VIQ and PIQ. Conclusions: The results of this investigation suggested that one or two dosages of antenatal dexamethasone is safe for the use of inevitable preterm birth. © 2012 Informa UK, Ltd.