In 1974, seven cases of human echinococcosis were diagnosed in Arizona and New Mexico. A retrospective survey of Arizona and New Mexico hospitals obtained data on ten additional cases reported for the 5-year period 1969 through 1973. Sixteen cases were diagnosed as Echinococcus granulosus infections and one as E. multilocularis infection. The latter infection was in an Eskimo from Alaska, where E. multilocularis is endemic. All of the 16 E. granulosus cases were probably acquired autochthonously; 14 were diagnosed in American Indians of the Navajo (8 cases), Zuni (4 cases), and Santo Domingo (2 cases) tribes; the remaining 2 cases were diagnosed in non-Indian women. This is the first published account of echinococcosis autochthonous to Arizona and New Mexico. Evidence suggests that the infection may have been introduced only relatively recently to the areas populated by the American Indians and that parasite transmission to humans is increasing.