The purpose of the study was to analyse for the first time the validity of a slightly modified version of the Portuguese Postpartum Depression Screening Scale (PDSS), to be used as a screening instrument for antenatal depression. Specifically, the aims were to analyse its psychometric properties, to determine PDSS cutoff points and associated conditional probabilities to screen for depression according to DSM-IV and ICD-10 criteria and to compare its screening performance with that of the Beck Depression Inventory-II (BDI-II). Five hundred and three pregnant women in the third trimester of pregnancy completed both questionnaires and were interviewed face-to-face with the Portuguese version of the Diagnostic Interview for Genetic Studies. The Portuguese version of the Operational Criteria Checklist for Psychotic Illness was used to obtain DSM-IV and ICD-10 diagnoses of depression, our gold standards for caseness. PDSS reliability and validity were very good and comparable to those obtained in the postpartum validation studies developed in Portugal and in other countries, showing satisfactory sensitivity and specificity combinations (80%). Compared with BDI-II, it has the advantage of being more specific for the motherhood context. Although developed for postpartum depression, PDSS is accurate to screen for antenatal depression, and it could be very useful for clinical and epidemiologic purposes.