This study was undertaken to determine the point prevalence of psychiatric disorders during the second trimester of pregnancy in a population-based sample of pregnant women. Participants were 1795 consecutive pregnant women attending routine ultrasound screening at two obstetric clinics in Northern Sweden during 1 year. The Primary Care Evaluation of Mental Disorders (PRIME-MD) was used for evaluating. Overall, 1734 (96.6%) of the women filled in the PRIME-MD patient questionnaire. Psychiatric disorders were present in 14.1% of the women. Major depression was prevalent in 3.3% of patients and minor depression in 6.9% of patients. Anxiety disorders were encountered in 6.6% of patients. Women with psychiatric disorders displayed significantly more somatic symptoms and more pronounced fear of childbirth. Among diagnosed patients, only 5.5% had some form of treatment. The prevalence of mood and anxiety disorders in this unselected population of pregnant women was high and the majority of the women were found to be undiagnosed and untreated.