A case of progressive diaphyseal dysplasia (Engelmann's disease) is described in a 23-year old woman. The disease is characterized by limb pain, muscular wasting, a waddling gait and easy fatiguability. It is diagnosed radiologically by cortical thickening, a narrowed medullary cavity, and increased diameter of the diaphyses of the long bones. The extension of the bone lesions was evaluated by scintigraphy using 99mTc methylene diphosphonate (MDP) and 99mTc colloids. Corticosteroid treatment resulted in clinical improvement and reduction of the diaphyseal uptake of MDP and colloids.