Apparently conflicting results have been reported regarding the incidence, and even the existence, of endometriosis in visually normal peritoneum. The present study was undertaken in view of the fact that the presence and incidence of nonvisualized deep and/or microscopic endometriosis may be of importance in patient management. One patient in this study demonstrated a 1-mm lesion of endometriosis beneath visually normal peritoneum. Two additional patients had cellular surface zones of possible endometrial stroma without a contiguous epithelial component. The results support the existence of unrecognized subperitoneal and microscopic surface endometriosis.