The Great Crested Flycatcher is most similar to the other flycatchers in the genus Myiarchus: Brown-crested, Ash-throated and Dusky-capped. It has a darker gray throat and breast than the other species and has a pale base to its lower mandible. Ash-throated and Dusky-capped are smaller. Ash-throated has paler yellow underparts. Brown-crested and Dusky-capped have browner tails. The calls of these very similar species are an excellent way to distinguish them. Some species of kingbirds are similar but have paler heads and lack rusty in the tail.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.