We report a patient with melorheostosis in whom increased procollagen alpha1(I) mRNA expression and alpha1(I), alpha2(I) and alpha1(III) collagen secretion were observed in dermal fibroblasts obtained from a skin biopsy overlying the involved bone. The patient was a 53-year-old man with melorheostosis lesions over the left knee joint. Multiple pigmented macules were present on the medial aspect of the lower left leg. Hyperpigmentation of the basal keratinocytes, thick-walled vessels in the reticular dermis, and proliferation of normal-appearing collagen around the hair follicles were observed histologically.