The breeding systems employed by wild plant populations have profound effects on their genetic structure and evolution, yet remain unknown or incompletely described for many species. Linum sulcatum Riddell (Linaceae) is an herbaceous annual native to eastern North America. This species is thought to be self-compatible, but there has been no experimental evidence to date to support this claim. To assess the breeding system of this species, seeds were collected from wild populations and reared in a controlled environment. Various floral treatments were conducted to determine the self-compatibility of this species and the mode of selfing used. Additional controlled within- and between-population crosses were conducted to determine the relative degree to which this species can outcross. Self-fertilization was highly successful and appears to be achieved autonomously. Outcrossing success was very limited, suggesting this species may exhibit some degree of cross-incompatibility. Furthermore, a separate experiment that examined pollen tube growth found that self-pollination resulted in the formation of more pollen tubes relative to cross-pollination and that complete pollen tube growth can occur less than two hours following self-pollination. This information is relevant to the future persistence of this species, as much of its remaining habitat is distributed among small, highly fragmented patches subjected to current and future environmental change.