Plethodon stormi and Plethodon elongatus are two closely related species of plethodontid salamanders that are restricted to the Klamath Province of northwestern California and southwestern Oregon. Discovery of three localities south of the Klamath River, in the Scott River drainage, not assignable to either P. elongatus or P. stormi, motivated closer examination of this complex. We describe molecular (mitochondrial DNA) and morphological variation among specimens collected from the three newly discovered populations and compare these to populations of P. elongatus and P. stormi from Siskiyou County, California and Jackson and Josephine Counties, Oregon. Analyses of mitochondrial sequence data from the ATPase 6 and cytochrome b genes recovered clades corresponding to P. elongatus, P. stormi and the Scott River populations. Multivariate analyses indicate that Scott River drainage animals are morphologically distinct from P. elongatus and P. stormi. Because both genetic and morphological data indicate that the Scott River populations are distinctive, we provide a description of a new species, Plethodon asupak, to reflect the evolutionary history of this group and facilitate species management.