Endometriosis is a painful chronic female disease defined by the presence of endometrial tissue implants in ectopic locations. The pathogenesis is much debated, and type I interferons could be involved. The expression of genes of the type I interferon response were profiled by a specific PCR Array of RNA obtained from ectopic and eutopic endometrium collected from 9 endometriosis patients and 9 healthy control women. Transcriptional expression levels of selected interferon-regulated and housekeeping genes were investigated by real-time quantitative reverse transcriptase PCR (qRT-PCR). Stably expressed housekeeping genes for valid normalization of transcriptional studies of endometrium and endometriosis have not yet been published. Here, seven housekeeping genes were evaluated for stability using the GeNorm and NormFinder software. A normalization factor based on HMBS, TBP, and YWHAZ expression was suitable for normalization of qRT-PCR studies of eutopic vs. ectopic endometrium. In the endometrial cell lines HEC1A, HEC1B, Ishikawa, and RL95-2, HMBS and HPRT1 were most stably expressed. The interferon-specific PCR Array indicated significantly different expression of the genes BST2, COL16A1, HOXB2, and ISG20 between the endometrial tissue types. However, by correctly normalized qRT-PCR, levels of BST2, COL16A1, and the highly type I IFN-stimulated genes ISG12A and 6-16 displayed insignificant variations. Conversely, HOXB2 and ISG20 transcriptions were significantly reduced in endometriosis lesions compared with endometrium from endometriosis patients and healthy controls. In conclusion, appropriate housekeeping genes for normalization of qRT-PCR studies of endometrium and endometriosis have been identified here. Abolished expression of ISG20 and HOX genes could be important in endometriosis.