['All women delivering a preterm infant should receive antenatal corticosteroid prophylaxis, but many miss this opportunity. We determined the risk factors associated with missed prophylaxis in a geographically defined area of Italy.', 'We prospectively studied all mothers who delivered babies between 24 and 31 completed weeks of gestation, from 2009 to 2013, in all maternity units in Tuscany.', 'Of 1232 mothers, 186 (15.1%) did not receive prophylaxis. The risk was higher in migrant mothers, with an adjusted risk ratio (RR) of 1.28 and 95% confidence interval (95% CI) of 1.04-1.56, and in mothers hospitalised for less than 24 hours (RR 4.09, 95% CI: 2.90-5.78). Preterm prelabour rupture of membranes (RR 0.63, 95% CI: 0.41-0.96) and maternal antepartum transfer (RR 0.24, 95% CI: 0.18-0.32) were protective. Hospital level at birth and gestational age did not influence the prophylaxis rate. The population-attributable fractions were 50.4% for late hospital admissions and 10.2% for migrant status.'] Does area-based study identify risk factors associated with missed antenatal corticosteroid prophylaxis in women delivering preterm infants?