Purpose: The purpose of this study was to pilot a stepped collaborative care intervention for women with postpartum depression and evaluate health differences between self-diagnosed depressed and nondepressed women. Methods: Five hundred six mothers of infants from 7 clinics completed surveys at 0 to 1, 2, 4, 6, and 9 months postpartum and a Structured Clinical Interview for DSM-IV (SCID). SCID-positive depressed women were randomized to stepped collaborative care or usual care. Nine-month treatment, health, and work outcomes were evaluated for stepped care women (n = 19) versus control depressed women (n = 20), and self-diagnosed depressed women (n = 122) versus nondepressed women (n = 344). Results: Forty-five women had SCID-positive depression whereas 122 had self-diagnosed depression. For SCID-positive depressed women, the stepped care intervention increased mothers' awareness of their depression diagnosis (100% vs 61%; P = .008) and their receipt of treatment (94% vs 56%; P = .019). Self-diagnosed depressed women (vs nondepressed women) had more depressive symptoms and acute care visits, worse general and mental health, and greater impact of health problems on regular activities. Conclusions: The stepped care intervention improved women's knowledge of their postpartum depression diagnosis and their receipt of treatment. However, our formal diagnostic procedures missed many women whose depressed mood interfered with their health and function.