BACKGROUND: Chronic lung disease (CLD) remains a major problem in neonatal intensive care units. Persistent inflammation in the lungs is the most likely underlying pathogenesis. Corticosteroids have been used to either prevent or treat CLD because of their potent anti-inflammatory effects. OBJECTIVES: To determine if postnatal corticosteroid treatment is of benefit in the prevention of chronic lung disease (CLD) in preterm infants. This review examines the outcome of trials where preterm infants at risk of CLD were given postnatal corticosteroids within the first seven days of life. SEARCH STRATEGY: Randomised controlled trials (RCTs) of postnatal corticosteroid therapy were sought from the Cochrane Controlled Trials Register, MEDLINE (1966 - May 2008), hand searching paediatric and perinatal journals, examining previous review articles and information received from practising neonatologists. Authors of all studies were contacted, where possible, to confirm details of reported follow-up studies, or to obtain any information about long-term follow-up where none had been reported. SELECTION CRITERIA: Randomised controlled trials of postnatal corticosteroid treatment within the first 7 days of life (early) in high risk preterm infants were selected for this review. Most studies evaluated the use of dexamethasone but we also included studies that assessed hydrocortisone, even if it was used to manage hypotension. DATA COLLECTION AND ANALYSIS: Data regarding clinical outcomes including mortality, CLD (including late rescue with corticosteroids, and need for home oxygen therapy), death or CLD, failure to extubate, complications during the primary hospitalisation (including infection, hyperglycaemia, hypertension, pulmonary air leak, patent ductus arteriosus (PDA), severe intraventricular haemorrhage (IVH), periventricular leucomalacia (PVL), necrotising enterocolitis (NEC), gastrointestinal bleeding, intestinal perforation, severe retinopathy of prematurity (ROP), and long-term outcome (including blindness, deafness, cerebral palsy and major neurosensory disability) were abstracted and analysed using RevMan 5. MAIN RESULTS: Twenty-eight RCTs enrolling a total of 3740 participants were eligible for inclusion in this review. A meta-analysis of these trials demonstrated significant benefits as regards earlier extubation and decreased risks of CLD at both 28 days and 36 weeks' postmenstrual age (PMA), death or CLD at 28 days and 36 weeks' PMA, PDA and ROP, including severe ROP. There were no significant differences in the rates of neonatal or subsequent mortality, infection, severe IVH, PVL, NEC or pulmonary haemorrhage. Gastrointestinal bleeding and intestinal perforation were important adverse effects and the risks of hyperglycaemia, hypertension, hypertrophic cardiomyopathy and growth failure were also increased. In the twelve trials that reported late outcomes, several adverse neurological effects were found at follow-up examinations including developmental delay (not defined), cerebral palsy and abnormal neurological examination. However, major neurosensory disability was not significantly increased, either overall in the seven studies where this outcome could be determined, or in the two individual studies where the rates of cerebral palsy or abnormal neurological examination were significantly increased. Moreover, the rates of the combined outcomes of death or cerebral palsy, or of death or major neurosensory disability were not significantly increased. Dexamethasone was the drug used in most studies (n = 20); only eight studies used hydrocortisone. In subgroup analyses by type of corticosteroid, most of the beneficial and harmful effects were attributable to dexamethasone; hydrocortisone had little effect on any outcomes except for an increase in intestinal perforation and a borderline reduction in PDA. AUTHORS' CONCLUSIONS: The benefits of early postnatal corticosteroid treatment (</= 7 days), particularly dexamethasone, may not outweigh the known or potential adverse effects of this treatment. Although early corticosteroid treatment facilitates extubation and reduces the risk of chronic lung disease and patent ductus arteriosus, it causes short-term adverse effects including gastrointestinal bleeding, intestinal perforation, hyperglycaemia, hypertension, hypertrophic cardiomyopathy and growth failure. Long-term follow-up studies report an increased risk of abnormal neurological examination and cerebral palsy. However, the methodological quality of the studies determining long-term outcomes is limited in some cases; the surviving children have been assessed predominantly before school age, and no study has been sufficiently powered to detect important adverse long-term neurosensory outcomes. There is a compelling need for the long-term follow-up and reporting of late outcomes, especially neurological and developmental outcomes, among surviving infants who participated in all randomised trials of early postnatal corticosteroid treatment. Hydrocortisone in the doses and regimens used in the reported RCTs has few beneficial or harmful effects and cannot be recommended for prevention of CLD.