Ovarian cancer occurs in 20,000 American women per year, 12,000 of whom will die from this disease. Oral contraceptives (OCs) which are commonly used, have been shown to protect against the development of ovarian cancer. However, up until now, we have known little about the persistence of the OC effect after cessation of use, the importance of age at first use, an the impact of estrogen/progestin potency on ovarian cancer as a whole, or on different pathologic types of ovarian cancer. Because women exposed to the pill are just entering the period of highest risk for ovarian cancer, we now have the first opportunity to examine these important issues in detail. The overall objective of this project is to evaluate the relationship between long-term combination oral contraceptive (OC) use and the subsequent development of epithelial ovarian cancer. Additionally, this study will allow the efficient evaluation of other possible risk factors for ovarian cancer. The proposed study is a population-based case-control investigation. One thousand hospitalized incident cases of ovarian cancer will be compared to two thousand community controls without the disease who will be selected randomly from the community using random digit dialing. The controls will be frequency matched to the expected age distribution of the cases using five year age strata. All study subjects (cases and controls) will undergo a structured in-person home interview. In addition, they will have their medical records reviewed in order to validate their medical history and information on prescription drugs received. Finally, they will have pathology slides reviewed by the study pathologist in order to verify the diagnosis of epithelial ovarian cancer and to classify cancers by histologic type. The occurrence of potential risk factors will be compared for epithelial ovarian cancer cases and controls in age-adjusted and multivariate adjusted analyses. The importance of enhancing our understanding regarding the relationship between OCs and ovarian cancer is twofold. First, OCs represent a potentially important modifiable protective factor. Second, further understanding of this relationship will help to clarify the pathogenesis of ovarian cancer. Equipped with an epidemiologically supported etiologic hypothesis, scientists can develop biologic studies more accurately targeting the process of pathogenesis, and health providers can precisely aim prevention strategies.