OBJECTIVE To explore the proportion and characteristics of women with a mental disorder who have contact with mental health services during pregnancy and the postnatal period in a maternity service in London. METHODS Data from the WEll-being in pregNancy stuDY (WENDY), a prospective cohort study, were used. Women were recruited at their first appointment for antenatal care and assessed for mental disorders using the Structured Clinical Interview DSM-IV Axis I/II Disorders for Research. Clinical, sociodemographic and psychosocial characteristics were collected. Mental health service use data were collected for the period from study entry to 3 months postpartum. RESULTS Two hundred women met diagnostic criteria for a mental disorder. Fifty-five (34%) of these had at least one contact with mental health services. Moderate depression (OR 7.44, CI 2.03-27.28, p < 0.01), severe depression (OR 10.5, CI 2.68-41.12, p < 0.01), past psychiatric hospital admission (OR 3.76, CI 1.05-13.44, p < 0.05), symptoms of anxiety (OR 3.95, CI 1.86-8.37, p < 0.001) and perceived low levels of social support (OR 0.43, CI 0.18-1.01, p = 0.05) were associated with an increased likelihood of contact with mental health services in univariate analyses. However, only moderate (OR 5.92, CI 1.31-26.78, p = 0.02) and severe depression (OR 6.04, CI 1.08-33.72, p = 0.04) remained significant in the multivariate regressions analyses. CONCLUSIONS Only a third of women with a diagnosable mental disorder at their first antenatal appointment had any contact with mental health services during pregnancy or up to 3 months postpartum. Further research is warranted to elicit perinatal women's views about the potential barriers to accessing professional mental health care.