A previously unrecognized partial skeleton of Chirostenotes pergracilis Gilmore, 1924 from the Upper Cretaceous Horseshoe Canyon Formation of Alberta (Canada) includes parts of the skull, much of the pelvic girdle, and elements from all regions of the vertebral column. It provides much new information concerning the skeletal structure of this unusual theropod dinosaur. Close structural correspondence between the maxilla of this specimen and the mandible of Caenagnathus collinsi R. M. Sternberg, 1940 indicates that the latter taxon should be considered a subjective junior synonym of Chirostenotes pergracilis. “Ornithomimus” elegans Parks, 1933 is probably also referable to Chirostenotes. The family-level taxon Elmisauridae Osmólska, 1981 is regarded as a subjective junior synonym of Caenagnathidae R. M. Sternberg, 1940. The newly recognized specimen of Chirostenotes pergracilis provides important new evidence for referring Caenagnathidae to Oviraptorosauria. Preliminary phylogenetic analysis indicates a sister-group relationship between Oviraptorosauria and Therizinosauroidea.