This study reports a longitudinal prospective study of the impact of an unwanted pregnancy on the mental health of the mother. Data are derived from a Brisbane, Australian sample of 8556 mothers who were enrolled at their first clinic visit (mean gestation 18 weeks) and then interviewed again some 3-5 days after the birth and when the baby was 6 months of age. Standard scales of mental health were administered on each of these occasions and mothers whose babies were unwanted were compared with the rest of the sample.The results indicate that mothers of unwanted children have somewhat higher rates of anxiety and depression than the comparison group, but that the magnitude of the mental health differences between the two groups: (a) diminishes over the period of the follow-up, (b) may be partly attributable to the prior poor mental health of women giving birth to an unplanned and unwanted baby, (c) is such that relatively few women who give birth to an unwanted baby experience mental health problems.The paper considers the implications of these results for health planners, notes the absence of contrary data and the need to acknowledge that these results may reflect situational factors which are characteristic of but not necessarily limited to Brisbane.