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Elastofibroma is a rare, benign, fibrous tumor formed by the proliferation of characteristic elastic fibers that commonly occurs between the lower margin of the scapula and the ribcage. We undertook a histochemical, immunohistochemical, and ultrastructural study of an elastofibroma dorsi beneath the right scapula of a 77-year-old woman. Tumor cells comprised collagen fiber bundles, numerous elastic fibers, and spindle cells resembling fibroblasts. The elastic and collagen fibers in the tumor were stained positively with Elastic van Gieson and Masson trichrome staining, respectively. Immunostaining showed that the fibroblasts were strongly positive for CD34, positive for vimentin, and weakly positive for α-smooth muscle actin. Ultrastructural observations revealed elastin and microfibrils between numerous irregularly arranged collagen fiber bundles. Signs suggestive of elastin deposition were also evident in the tangled collagen fibers themselves. The fibroblasts contained a large amount of rough endoplasmic reticulum and were surrounded on the outside of cells by microfibrils and collagen fibers. Although fibroblasts may produce large quantities of elastin, microfibrils, and collagen, our findings suggested that the deposition of elastin on collagen fibers may be involved in the formation of abnormal elastic fibers.