Relations between courtship success, aggressive success, and body size were examined in a laboratory study of the lekking Hawaiian fly, Drosophila silvestris. Courtship was studied by placing one male and one female in a cage together at a time, and aggression was observed with caged pairs of males. Aggressive success was positively and highly significantly correlated with body size, but uncorrelated with courtship success. Surprisingly, courtship success was negatively correlated with body size, although this relationship was not significant. Courtship success and aggressive success were not correlated. These results suggest that selection favors an intermediate optimum body size in this species.