Evidence is presented that suggests a genetic relationship between the Klamath and Sahaptian languages. The current list of potential Klamath-Sahaptian cognates contains core lexical material sufficient to demonstrate the validity of a genetic relationship, although many details of sound correspondence have yet to be worked out. But it is not only in core lexical materials that Klamath and Sahaptian are related. It is the purpose of this paper to show that these languages also share enough grammatical morphology to make a convincing case by itself. Analysis is presented in the following areas: kinship terms, NP case markings, pronominal morphology, interrogative and relative pronouns, third person referent tracking, verbal morphology, directions, object selection, tense-aspect-modality, morphological causatives, and classificatory prefixes. Contains 20 references. (LB)