Fifty-one records of patients with delayed postpartal uterine hemorrhage were studied from a total of 20,651 deliveries during a 10-year period. After reviewing the literature and analyzing the records, the authors propose that retained placental tissue is the most likely basic cause for the delayed bleeding as well as for the histologic picture labeled subinvolution or noninvolution of the placental site. Suggestions for therapy are offered and include the prophylactic use of manual exploration of the uterus immediately postpartum in all parturients as well as preoperative curettage before planned hysterectomy.