BACKGROUND:Many women who suffer from postnatal depression are never diagnosed or treated. The objective of this study was to develop an index for use in maternity settings that identifies women who may be at risk for postnatal depression. METHODS:Women (n = 1762) attending the "booking-in" clinic were screened for antenatal risk factors for postnatal depression. On the third postnatal day eligible women were screened for postnatal risk factors. The Edinburgh Postnatal Depression Scale was mailed to participants 16 weeks after the birth. A predictive index was developed, based on the mean Edinburgh Postnatal Depression Scale scores for each risk factor. The sensitivity, specificity, positive predictive value, and negative predictive value were used to assess the diagnostic value of the index. RESULTS:Seven hundred and twenty-three (50.1%) of the eligible women completed all phases of the study. Of this group, 93 (12.2%) women scored higher than 12 on the Edinburgh Postnatal Depression Scale. At a cutoff of 6, the index had positive predictive value of 39.8 percent for postnatal depression, a threefold improvement over the base rate. CONCLUSION:The Brisbane Postnatal Depression Index provides a clinically useful method for identifying women at risk for developing postnatal depression. It has applications for early intervention or to identify high-risk groups for research purposes.