We describe a histologic feature useful in the diagnosis of endometrial polyps, namely, the parallel arrangement of the endometrial glands' long axis to the surface epithelium (PGE). Polyps that are removed intact are usually easy to diagnose because of the polypoid appearance plus surface epithelium on all sides. In addition, there are thick-walled blood vessels and irregularly shaped glands. Rarely are all or even some of the characteristic features easy to identify in biopsies and curettage specimens. We evaluated 76 cases of grossly identifiable polyps from hysterectomy or polypectomy (working group) for various histologic features and tested the validity of those findings with another 75 specimens (test group), which had been diagnosed as polyps in another institute by separate investigators. The frequency of the various histologic features in the polyps varied depending on the menstrual state, shape, and histologic types of the polyps. PGE was found in 80% (40 of 50 polyps) of premenopausal women as the most common histologic feature, but it was less common in postmenopausal women (42%, 11 of 26) (P = 0.001). All functional polyps (100%, 19 of 19), many of hyperplastic polyp (65%, 20 of 31), and some fibrous polyps (38%, 8 of 21) showed the change. In premenopausal women, incidence of PGE was significantly different by the polyp's shape or histologic types (P < 0.05), but not in postmenopausal women. PGE was not identified in any of the 56 normal background endometria, even though the surface was often undulated. Almost identical findings were observed in the series from the test group, confirming the validity of this new finding. In summary, PGE, if present, is a useful histologic finding in facilitating the diagnosis of endometrial polyp in curettage specimens.