Background: The objectives of this study were to develop an education intervention about perinatal depression tailored to the information needs of primiparous women, to deliver this intervention antenatally, and to conduct a randomized controlled trial to determine the effect of the antenatal education intervention in the reduction of postnatal depression. Method: A prospective, randomized controlled trial of the education intervention (N=206) was conducted at three sites in Australia. The outcome of changes in mood state was measured by the Profile of Mood States questionnaire once antenatally (12-28 wk), and twice postnatally (8-12 and 16-24 wk); social support and demographic data were also collected. The education package was administered to the intervention group at the antenatal assessment of mood. Results: A significant and steady reduction in scores (overall and on the subscales) was observed over time for both groups, which showed significant improvement in symptoms of depression. No difference was detected when comparing the intervention group with the control group. Additional multivariate regression analyses revealed no relevant influence of social support or demographic variables. Conclusions: Women in both the intervention and control groups were more depressed antenatally than postnatally. Implications for assessment and management of mood states in women during the perinatal period are discussed.