Abstract
A papillary mucinous cystadenoma of the ovary with unique benign epithelial atypia is presented. the tumor was removed from a 33-year-old puerperal woman. Morphologically, the lining epithelium of the cystadenoma strikingly resembled the so-called Arias-Stella reaction of the endometrial epithelium, a benign cellular atypia produced by chorionic tissue during pregnancy. the atypical epithelium of the endometrium is known to persist several weeks after parturition or abortion, and should not be misinterpreted as malignancy.