Four aggregation sites for male Cephenemyia trompe Modeer were studied in the Kluane Game Sanctuary, southwest Yukon. All sites were well-defined topographical peaks at considerable distances (usually greater than 1 km) from one another. Males rested on the rocks and vegetation and individuals made frequent flights to investigate passing insects, presumably in search of a female. Male flies were active at the sites on element days; activity was a function of both temperature and light intensity. Flies remained at a particular site at least throughout the day but did not defend individual territories.