Characteristics such as courtship displays and body size have been shown to influence mating success of male fishes. However, few examples of structural sexual ornaments exist, and ornamentation is typically limited to coloration. One possible example of a structural sexual ornament in fishes may be the exaggerated opercular flaps of male longear sunfish (Lepomis megalotis). We investigated female mate choice in two laboratory experiments by manipulating opercular flap lengths of males by clipping and by applying artificial extensions. Females spent significantly more time with, and displayed more to the longer-flapped males in both experiments. These results suggest that the opercular flaps of male longear sunfish may function as sexual ornaments.