Papillary syncytial change (PSC) of endometrial epithelium, often regarded as a metaplastic change, shows syncytial to papillary aggregates of eosinophilic cells along the surface epithelium. To determine the cause and significance of PSC, 250 consecutive endometrial biopsy and curettage specimens and curettings in patients with suspected endometrial abnormalities were reviewed. Papillary syncytial change was found in 43 (17%) of the cases. Often PSC was focal, but in 12 cases it was multifocal and in 7 cases it was extensive. Patients with PSC ranged from 22 to 86 years of age. The primary pathologic findings in endometria with PSC included a variety of benign organic lesions and hyperplasia, as well as proliferative and secretory changes that suggested dysfunctional bleeding. One consistent finding in all cases was associated active endometrial bleeding with glandular and stromal breakdown, cell necrosis, and neutrophils in close proximity to PSC. Immunohistochemical study of 6 cases with extensive PSC showed no difference in reactivity to high and low molecular weight keratin, vimentin, and carcinoembryonic antigen compared with surrounding unaffected epithelium. The association of PSC with endometrial breakdown in a variety of conditions suggests that PSC is a benign retrogressive alteration rather than a metaplastic transformation to another cell type. Papillary syncytial change appears to be a useful histologic marker of acute endometrial breakdown and bleeding, and recognition of this phenomenon will prevent misclassification of this relatively common finding.