The first detailed description of the lambeosaurine Lambeosaurus magnicristatus (Ornithischia: Hadrosauridae) confirms that it is a distinct taxon characterized by its comparatively enormous cranial crest, formed predominantly by the caudodorsal process of the premaxilla, and an acute crest-snout angle. The holotype of L. magnicristatus occurs stratigraphically higher than all other Dinosaur Park Formation lambeosaurines at the Dinosaur Provincial Park locality. The only referred specimen was collected over 170 kilometers southeast of the type locality. Correlation of its host stratum with the well-known Dinosaur Park section reveals that L. magnicristatus has no biostratigraphic overlap with L. lambei and suggests that it replaces L. lambei on a regional scale in southern Alberta at the end of ‘Dinosaur Park time.’ Species-level phylogenetic analysis of Lambeosaurinae corroborates the monophyly of Lambeosaurus. The genus is characterized by five apomorphies, including a procumbent crest, complete enclosure of the ophthalmic canal of the laterosphenoid, the presence of a flange on the caudodorsal process of the premaxilla that overlaps the nasal in the rostral region of the crest, caudal extension of the premaxilla such that it forms the caudal margin of the crest, and a unique joint between the rostral nasal and the caudodorsal process of the premaxilla. Lambeosaurine phylogeny indicates that the development of a hypertrophied cranial crest evolved independently at least three times within the clade, suggesting that the crest enlargement is a recurring evolutionary trend within Lambeosaurinae.