RMRP is a non-coding RNA that is ubiquitously expressed in both humans and mice. RMRP mutations that lead to decreased RMRP levels are found in the pleiotropic syndrome Cartilage Hair Hypoplasia. To assess the effects of deleting RMRP, we engineered a targeting vector that contains loxP sequences flanking RMRP and created hemizygous mice harboring this engineered allele (RMRP conditional). We found that insertion of this cassette suppressed RMRP expression, and we failed to obtain viable mice homozygous for the RMRP conditional allele. Furthermore, we were unable to obtain viable homozygous RMRP null mice, indicating that RMRP is essential for early embryonic development.