Populations of the gynodioecious, self-compatible perennial Silene vulgaris (bladder campion) in northern Michigan were studied in 1981 and 1982 to compare aspects of fitness between females and hermaphrodites. Although theoretical arguments predict greater reproductive output by females, hermaphrodites produced more flowers and fruit per plant (63.6 +/- 14.8 vs. 37.8 +/- 9.8 flowers and 30.5 +/- 6.5 vs. 23.0 +/- 4.5 fruit). Hermaphrodites produced 2.5 times as many seeds per plant as did females. Ovules per ovary and seeds per capsule did not differ between the two breeding types. Although hermaphrodites had a greater probability of buds maturing into flowers, a greater proportion of female flowers developed into fruit (.814 +/- .035 vs. .54 +/- .042). Despite differences in corolla size, no differences between the sexes have been observed in nectar production or pollinator preference. Seeds from outcrossed parentage showed greater germination success than did those from selfed individuals obtained by artificial crosses. This suggests that maintenance of females may also be due to quality of the offspring in addition to traits of the adults. Differences in fitness of offspring of hermaphrodites (selfed) and females (obligately outbred) may contribute to maintenance of females despite greater hermaphrodite seed production, depending on pollinator behavior and outcrossing rates.