This study evaluates the effects of prenatal genetic group counselling on women's anxiety, decisional conflict and levels of knowledge. Participants (N=271) were aged 35 years and older. The results indicated that pre/postcounselling scores for anxiety did not change significantly, while decisional conflict decreased significantly. Pre/postcounselling scores on two different knowledge measures were analysed using 2x3 mixed ANOVAs for time by highest level of education and by having discussed prenatal diagnosis with one's health care provider. No potential interactions were statistically significant; time alone had a strong significant effect for both knowledge measures, suggesting that the effects of the counselling intervention were robust. Group genetic counselling is an effective method for education and decision support in the prenatal context, and may serve as a model for other clinical populations facing genetic screening decisions.