Phylogeography of northern populations of the Pacific treefrog, Pseudacris regilla, was investigated using mitochondrial cytochrome b sequence data (725 bp). Thirty-six haplo-types were detected among 59 samples collected from 20 populations. Two divergent coastal and inland clades were supported by several phylogenetic analyses including maximum parsimony, maximum likelihood, and Bayesian methods. Sequence differences among these clades ranged from 5.0 to 6.5%, suggesting they diverged during the Pliocene (approximately 3 MYA), coinciding with High Cascade orogeny and subsequent xerification of the Columbia Basin. Further, haplotype divergence within each clade was lower (0 to 1.8%), possibly as a consequence of population reduction during the Pleistocene. The overall pattern of divergence was not detected by previous morphological and protein analysis and is concordant with many other Northwest taxa. These results do not support previous intraspecific classification schemes, indicating the need for further examination of the taxonomic status of the coastal and inland clades.