The peritoneum is the matrix where benign and malignant proliferation of secondary müllerian epithelium occur. Endometriosis, endosalpingiosis, and endocervicosis are benign peritoneal neoplasms corresponding to endometrioid, serous, and mucinous carcinomas. These latter are concentrated predominantly, although not exclusively in the ovary, and reasons for this localization are discussed. Exposure to talc, or perhaps to the asbestos that often contaminates it, occurs in the process of powdering during infancy and may be the major initiating factor in benign and malignant disorders of the secondary müllerian system. It can be anticipated that the incidence both of endometriosis and of ovarian tumors will be reduced in those women powdered with starch instead of talc during infancy, as well as by the continued use of ovulation-suppressing agents such as contraceptive steroids.