To evaluate the clinical utility of Tc-99m MIBI scan in the detection of residual thyroid tissue or metastatic lesion in postoperative thyroid cancer patients, we compared Tc-99m MIBI scan with I-131 diagnostic and therapeutic scan in 30 postoperative well-differentiated thyroid cancer patients. Thyroglobulin levels of both on and off thyroid hormone medication and antithyroglobulin antibody were tested [Tg(on), Tg(off)l Positive rates for I-131 diagnostic and Tc-99m MIBI scan were 81% and 68% respectively. Concordance between I-131 diagnostic and Tc-99m MIBI scan was observed in 15 cases; 12 positive and 3 negative respectively Among the 6 cases with negative I-131 diagnostic scan and positive Tc-99m MIBI scan, 4 were positive in the therapeutic I-131 scan. We concluded that Tc-99m MIBI scan maybe a useful complementary modality to the currently established method of I131 scan and serum thyroglobulin level in the detection of recurrent or metastatic thyroid cancer, especially in the case of negative I-131 diagnostic scan.