A 68-year-old man with small cell carcinoma of the lung and adenocarcinoma of the prostate underwent Tc-99m MDP bone scintigraphy for the evaluation of skeletal metastases. Bilateral symmetrical photon defects in both parietal bones of the skull were observed. The radiographs of the skull demonstrates biparietal thinning in the same area of the abnormality identified on bone scintigraphy. Although these findings in cancer patients can be mistaken for skeletal metastases, the symmetry and location of the photon defects are generally indicative of biparietal thinning.