Background: Mice with the cystic fibrosis transmembrane conductance regulator (Cftr) gene knocked out develop osteopenia. To determine whether this phenotype is present in cystic fibrosis mouse models with the Delta F508 Cftr mutation we assessed the femora of adult FVB/N Cftr(tm1Kth) and C57BL/6 cftr(tm1Kth) mice. Methods: Bone disease, relative to littermate controls, was measured using histology, densitometry and quantitative imaging. Results: C57BL/6 Cftr(tm1Kth) mice had shorter femurs and bones of lower volume due to thinner trabeculae, compared to wild type littermates. FVB/N Cftr(tm1Eur) mice also presented a lower bone volume which was due to significantly fewer trabeculae in this strain. Osteoblast and osteoclast numbers did not differ between CF and controls, for either of FVB/N Cftr(tm1Eur) or C57BL/6 Cftr(tm1Kth) mice. The bone architecture of FVB/N Cftr(tm1Eur) mice did not significantly differ from that of C57BL/6 Cftr(tm1Kth) mice. Conclusions: An osteopenic bone disease is evident in adult Delta F508-Cftr cystic fibrosis mouse models. (C) 2010 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.