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ASSTRACT.-The systematic relationships of the diurnal birds of prey (Falconiformes) are unresolved. The monophyly of the order has not been established, and the relationships of the families within the order and of genera within the three polytypic families are unclear. To derive a phylogeny for the order and to assess the usefulness of the syrinx for resolving the systematics of nonpasserines, I analyzed variation in syringeal morphology of genera within each of the currently recognized families in the order as well as among four orders of outgroups. The phylogeny derived from these syringeal data supports the monophyly of the Falconiformes. In addition, syringeal data provide strong support for the monophyly of three clades within the Falconiformes: the Cathartidae; the Falconidae; and an Accipitrinae-Sagittariidae-Pandioninae cluster. The Cathartidae are positioned as basal to the other two clades. Overall results indicate that syringeal morphology is conservative, with most of the informative variation occurring at higher systematic levels.