To determine the prevalence of diagnosed and/or treated postpartum depression and anxiety, records were extracted for 1 year after delivery from databases of outpatient diagnoses and prescriptions, for women in a health maintenance organization who had delivered a child from July 1997 through June 1998. For comparison, telephone interviews were conducted 5 to 9 months after delivery with random samples of women who delivered at 2 facilities from June 1998 through January 1999. Of the women interviewed, 11% met criteria for major depression during the first 4 months postpartum, and an additional 13% met criteria for probable depression at 5 to 9 months postpartum. In contrast 7.0% of the large cohort had a visit or prescription for depression. The 1-year prevalence rate for diagnosed and/or treated anxiety without depression was 3.8%; the rate at time of interview was 14.7%. Overall, less than 33% of women with substantial depression or anxiety symptoms were detected.