A 27-year-old woman with progressive diaphyseal dysplasia (Camurati-Engelmann disease) received pamidronate and corticosteroid therapy for bone pain. During therapy, disease activity was assessed serially using bone scintigraphy with Tc-99m HMDP. With pamidronate administration, the bone pain became worse and diaphyseal uptake of Tc-99m HMDP increased, whereas corticosteroid administration improved the bone pain and reduced the diaphyseal uptake. In this case, pamidronate and corticosteroid produced different effects. Bone scintigraphy allowed an objective assessment of the response to these treatments, accurately reflecting clinical symptoms.