Tight skin (Tsk) is an autosomal dominant mutation located on mouse chromosome 2 and is associated with an intragenic duplication of the fibrillin 1 (Fbn1) gene. Mutant mice (Tsk/+) display a tightness of skin in the interscapular region, lung emphysema, myocardial hypertrophy, skeletal overgrowth, and kyphosis. It is hypothesized in this study that in Tsk mice the mutation in Fbn1 alters bone cell metabolism. A detailed study of the Tsk skeletal phenotype revealed that Tsk mice have significantly longer femurs and axial skeleton as well as vertebral abnormalities. Cortical and trabecular bone volumes were significantly decreased in Tsk femurs from 2- and 4-month-old mice (13% and 39%, respectively) as well as trabecular thickness, number, connectivity, and surface area. These skeletal differences were also associated with a reduction in bone mineral density in mutant mice. Expression of the osteoblast-specific genes Col1a1, BSP and OC was examined in marrow stromal cell cultures at various time points. A decrease in the rate of maturation of the Tsk cells was indicated by a delay in the appearance of OC expression. These initial experiments demonstrated a significant role of the fibrillin 1 protein in the extracellular matrix of bone cells.