Many preclinical therapy studies have focused on a small number of well-described mouse allograft or human xenograft models that poorly represent the heterogeneity of human disease. Here we have assembled a panel of mouse mammary cell lines derived from spontaneously-arising mouse mammary tumors or from mammary tumors arising in genetically engineered mouse models. We used the Affymetrix Mouse Diversity Genotyping Array to address DNA copy number variation in the genomes of the cell lines of this panel. The resulting information about regions of amplification and deletion should help inform biological analyses as well as provide a reference for cell line authentication/identification. Affymetrix Mouse Diversity Genotyping arrays were used according to manufacturer's directions to analyze gDNA extracted from 27 mouse mammary cell lines of varying malignancy.