The taxonomic status of Peromyscus comanche Blair 1943 is herein taxonomically reviewed. The karyotype of P. comanche is given and compared with Peromyscus truei truei and Peromyscus difficilis nasutus. Morphological comparisons are made between a sample of P. comanche and one of P. truei from New Mexico. Chromosomal and morphological evidence indicate the affinities of P. comanche are with P. truei and not with P. difficilis, as previously suspected. The difficulties in classifying alloptaric populations are discussed. Peromyscus comanche is considered a subspecies of P. truei (Peromyscus truei comanche). Peromyscus comanche is one of three nominal species of the Peromyscus truei species group occurring in the southwestern United States. Peromyscus difficilis, the juniper mouse, occurs in Colorado, New Mexico, Utah, Arizona, Texas, and extreme western Oklahoma, and thence south into Mexico. Peromyscus truei, the pinon mouse, has a wider distribution extending from central Oregon south to Baja California, eastward to extreme western Oklahoma, and thence south to Oaxaca. The third species, P. comanche, occupies a restricted range along the rocky, cedar covered slopes along the Break of the Plains in western Texas (Blair, 1943). P. difficilis and P. truei are ecologically, altitudinally, and geographically sympatric over much of their range in the western United States. P. comanche is isolated by several miles of unsuitable habitat from the nearest known population of other mice of the truei group in New Mexico and Oklahoma. The three species are difficult to distinguish on the basis of morphology and are considered by some authors (notably Blair, 1943 and Tamsitt, 1961a) to be sibling species. Blair (1943) described P. comanche as a full species closely related to Peromyscus nasutus (now considered a subspecies of difficilis). Since Blair's description of comanche, the taxonomic status of the 1 Contribution No. TA 9988, Texas Agricultural Experiment Station, Texas A&M University.