The wheat stem sawfly is the most important insect pest of wheat in the northern Great Plains. Yield losses of up to 70% have been reported in parts of the US and Canada, with annual losses exceeding $50 million. An on-going biological control project is investigating the possible use of exotic parasitoids from Asia to control the wheat stem sawfly. The following study was initiated to provide baseline data on the impact and dynamics of endemic wheat stem sawfly natural enemies. Wheat stem sawfly populations in eastern Montana and western North Dakota were surveyed in 1999-2000. High density populations at six locations in northeastern Montana were monitored beginning in 2000. Infestations of more than 21% were observed each year at all locations except one, and fluctuated across years and locations. Two parasitoids, Bracon cephi and B. lissogaster (Hymenoptera: Braconidae), are key mortality factors for the wheat stem sawfly. Parasitism levels increased at all locations from 11 to 48% in 2000 to 42 to 84% in 2002, but declined in 2003. The impact of these natural enemies is inconsistent, as infestation levels at some sites remain high. The dynamics of Cephus cinctus, Bracon spp. and possible interactions with specific wheat cultivars is also discussed.