To evaluate epithelial ovarian cancer (EOC) risk factors by level of invasiveness and histology. A population- based epidemiologic case- control study of EOC was conducted over a 2- year period (January 2000 to December 2001) in 22 counties of Central California that comprise the reporting area for two regional cancer registries. Telephone interviews were conducted with 256 cases and 1122 control frequencies matched on age and ethnicity. The interview obtained information on demographic factors aswell as information pertinent to the respondent’ s menstrual and reproductive experience,use of exogenous hormones, surgical history, and family history of cancer. Adjusted odds ratios were calculated using stratification as well as Logistic regression methods. Analyses were completed by level of invasiveness and cell type. Strong protective associations were observed for use of oral contraceptives and parity. Risk increased with a family history of ovarian, but not breast cancer and age at first birth was positively associated with increased risk. Hormone replacement therapy was associated with increased risk only in long- term users. Many of the relationships were observed only in specific histologic subtypes of EOC. Risk of EOC is associated with several lifestyle and environmental exposures but the impact of these effects appears to be dependent upon level of invasiveness and histologic subtypes of EOC. However, the sample size available for analysis limits our statistical power and our ability to analyze data by histologic subtype, thus limiting interpretation of our results. A population-based epidemiologic case-control study of EOC was conducted over a 2-year period (January 2000 to December 2001) in 22 counties of Central California that include the reporting area for two regional cancer registries. The interview obtained information on demographic factors aswell as information pertinent to the respondent’s menstrual and reproductive experience, use of Exogenous hormones, surgical history, and family history of cancer. Adjusted odds ratios were calculated using stratification as well as Logistic regression methods. Analyzes were completed by level of invasiveness and cell type. Strong protective associations were observed for use of oral contraceptives and parity. Risk increased with a family history of ovarian, but not breast cancer and age at First birth was positively associated with increased risk. Hormone replacement therapy was associated with increased risk only in long- term users. Many of the relationships were observed only in specific histologic subtypes of EOC. Risk of EOC is associated with several lifestyle and environmental exposures but the impact of these effects appears to be dependent upon level of invasiveness and histologic subtypes of EOC. However, the sample size available for analysis limits our statistical power and our ability to analyze data by histologic subtype, thus limiting interpretation of our results.