The purpose of this study was to assess the effectiveness of a practical antenatal screen used at the Royal Women's Hospital, Brisbane, to identify women at risk for postnatal depression. It was a prospective, hospital-based, cohort study of 901 women (600 with and 301 without prenatal risk factors for postnatal depression). Depression was measured 16 weeks after the birth using the Edinburgh Postnatal Depression Scale. More of the women with a prenatal risk factor for depression (25.9%) scored above 12 on the Edinburgh Postnatal Depression Scale than those without any risk (10.9%) (p < or = 0.001). Low social support (p < or = 0.001), a personal history of mood disorder (p < or = 0.001) and a past history of postnatal depression ( p = 0.002) were all strongly associated with postnatal depression in this sample. Results indicate that an objective, psychosocial assessment during pregnancy improves recognition of women at risk for postnatal depression.