1. A case of melorheostosis with a nineteen-year follow-up, showing marked progression of the disease process, is reported.
2. Review of the literature reveals 131 cases of melorheostosis, the characteristics of which are defined.
3. Pathological specimens from two biopsies, eighteen years apart, suggested a progression from vasculitis to vascular obliteration with fatty and mucoid degeneration and muscle atrophy. Also seen was metaplastic cartilage formation within the mesenchymal tissue with cartilage degeneration and calcification which progressed to ossification. In the later specimens intramembranous-bone formation was noted. The etiology of this vascular damage remains unknown.