Background: This prospective study used both self-report (STAI) and clinical diagnostic interview (MINI-Plus) to examine the course of maternal anxiety across the transition to parenthood. The study also assessed i) the validity of the STAI for antenatal use in an Australian sample and ii) the relative utility of the MINI-Plus and STAI scales as antenatal measures of risk for postnatal anxiety and mood disorders. Methods: Participants were 100 women recruited during routine antenatal assessment at a major obstetric hospital in Sydney. An antenatal screening instrument (ANRQ) identified half the sample as being at "high risk" for developing postnatal anxiety and/or depression. Participants completed the STAI during the third trimester of pregnancy and the MINI-Plus was administered during pregnancy and during the seventh postnatal month to assess anxiety and depression meeting DSM-IV criteria. Results: The data indicated considerable stability in anxiety and depression from pregnancy through the postnatal period, as assessed by both diagnostic interview and maternal self-report. Antenatal anxiety meeting diagnostic criteria and antenatal trait anxiety exceeding a cut-off score of 40 on the STAI were both found to be significant predictors of postnatal anxiety and mood disorders (p-values < .05). Further analyses revealed that the measures were equivalent in their predictive utility. Finally, the STAI state and trait anxiety scales demonstrated a reasonable estimation of antenatal clinical state when tested against the MINI-Plus diagnostic interview during pregnancy. Conclusions: The findings from this study suggest that antenatal anxiety as assessed by either clinical interview or maternal self-report is an important predictor of postnatal anxiety and mood disorders. The validity of the STAI scales for use during pregnancy was also demonstrated for the first time in an Australian sample.