The aim of this study was to make a comparison between the uptake of Tc-99m MIBI and Tl-201 in evaluation of musculoskeletal lesions. Fourteen cases were studied. Each study consisted of a Tl-201 study followed by a Tc-99m MIBI scan. In addition, a whole-body bone scan was performed in each patient to visualize bone metastases. Tl-201 and Tc-99m MIBI uptakes were evaluated by visual assessment and by using lesion-to-background (L/B) ratio. The authors found increased Tl-201 uptake with a mean L/B ratio of 2.81 and less Tc-99m MIBI uptake with a mean L/B ratio of 2.18 in malignant lesions. Both agents showed lower uptake with mean L/B ratios of 1.6 and 1.2 in benign lesions, but there was no statistical difference between the uptakes of either Tl-201 or Tc-99m MIBI in those with malignant and those with benign lesions. In addition, false-positive imaging was observed with both Tl-201 and Tc-99m MIBI. The results demonstrated that Tl-201 and Tc-99m MIBI accumulations in musculoskeletal lesions are not specific for malignancy.