The proposition that mucinous ovarian cancer has an etiology distinct from that of other histologic types has been evaluated using data from a population-based case-control study of epithelial ovarian cancer conducted in 1990--1993 among Australian women aged 18--79 years. The protective effects of parity and oral contraceptive use were greater in nonmucinous than in mucinous ovarian tumors. However, these differences appeared to be driven largely by the effect of ovulatory life, which was positively associated with nonmucinous tumors only. An association with family history of breast and/or ovarian cancer also appeared to be restricted to nonmucinous cancers. These results lend support to the hypothesis that mucinous and nonmucinous ovarian tumors develop via different causal mechanisms.