This systematic review assessed the success of randomized controlled trials of preventative interventions for postnatal depression (PND). Outcomes examined were estimates of PND prevalence. Methodological quality was determined through the examination of key components individually with independent data extraction by all three authors. Data sources included Medline, PsycINFO, Sociofile, CINAHL, COPAC, EMBASE, Cochrane library; hand searches and a newsletter requests for unpublished trials to the Marcé Society and Postpartum Support International. Twenty-one RCTs were included in this review. Nine of these trials demonstrated short-term preventative success (seven psychological and supportive interventions, one unpublished antidepressant trial and a calcium carbonate trial) but none provided any evidence of long-term success. Furthermore, the results of three of the psychological intervention trials should be viewed with caution due to a lack of methodological rigour. There is a need for future research into the prevention of PND to be tightly designed and maybe include an exploration of the experience of postnatal depression for multiparous women.