Reported are two cases of oncogenic osteomalacia, each caused by a small mesenchymal tumor, with detailed assessment of the tumors by light microscopy, electron microsopy, and immunohistochemistry. One tumor was a primitive mesenchymal tumor with prominent giant cell and vascular components, and the second resembled the giant cell variant of soft parts chondroma. Osteoclast‐like, multinucleated giant cells and vascularity were prominent features in both tumors. Although the literature documents a histologically heterogeneous group of tumors as causing this syndrome, most have multinucleated giant cells and/or extensive vascularity. The high incidence of these two histologic features in this group of tumors suggests that either or both may be related to the pathogenesis and/or metabolic consequences of oncogenic osteomalacia/rickets.