The histologic types of epithelial ovarian cancer differ in clinical behavior, descriptive epidemiology, and genetic origins. The goals of the current study were to characterize further the relation of histologic- specific ovarian cancer risks to reproductive and lifestyle attributes. The authors conducted a pooled analysis of 10 case- control studies of ovarian cancer in US White women, involving 1834 patients with invasive epithelial ovarian cancer (1067 serous, 254 mucinous, 373 endometrioid, and 140 clear cell) and 7484 control women. Risks of all four histological types were inversely associated with parity and oral contraceptive use, but the histologic types showed different associations with nonreproductive factors. Unique associations include an inverse relation of serous cancer risk to body mass index, a positive relation of mucinous cancer risk to cigarette smoking, and a weakly positive relation of endometrioid cancer risk to body mass index. Risk of all histologic types was unassociated with age at menarche, age at menopause, a history of infertility, noncontraceptive estrogen use, and alcohol consumption. The most important modifiers of ovarian cancer risk (parity and oral contraceptive use) showed similar associations across the histologies. Nevertheless, the unique associations seen for other modifiers support the conjecture that the histologic types of epithelial ovarian cancer have different etiologies, which should be addressed in future investigations of the molecular basis of ovarian cancers and their responses to therapies. The histologic types of epithelial ovarian cancer differ in clinical behavior, descriptive epidemiology, and genetic origins. The goals of the current study were to characterize further the relation of histologic- specific ovarian cancer risks to reproductive and lifestyle attributes. The authors conducted a pooled analysis of 10 case-control studies of ovarian cancer in US White women, involving 1834 patients with invasive epithelial ovarian cancer (1067 serous, 254 mucinous, 373 endometrioid, and 140 clear cell) and 7484 control women. Risks of all four histological types were inversely associated with parity and oral contraceptive use, but the histologic types showed different associations with nonreproductive factors. of endometrioid cancer risk to body mass index. Risk of all histologic types was Yetassociated with age at menarche, age at menopause, a history of infertility, noncontraceptive estrogen use, and alcohol consumption. The most important modifiers of ovarian cancer risk (parity and oral contraceptive use )arently similarAGES across the histologies. seen for other modifiers support the conjecture that the histologic types of epithelial ovarian cancer have different etiologies, which should be addressed in future investigations of the molecular basis of ovarian cancers and their responses to therapies.