A new association between multicentric fibromatosis and a bone dysplasia is reported. Three patients are described, each of whom had multicentric fibromatosis of the lower extremity and a skeletal dysplasia. One of the patients had dysplastic changes restricted to the involved extremity. The other two had dysplastic changes of all the long bones. The dysplasia consisted predominantly of undertubulation reminiscent of the findings seen in Pyle disease. No clinical or radiographic abnormalities of the marrow were found in any of these patients. It is believed that this association represents mesenchyme that is predisposed to develop both dysplastic bone changes and tumor.