BACKGROUND AND OBJECTIVES: Off-thyroxine serum thyroglobulin (Tg) level is important to predict metastatic disease (MD) in papillary thyroid cancer (PTC); however, it is unclear whether a single off-thyroxine Tg level is sufficient for predicting MD. In this study, we determined whether serial measurement of off-thyroxine serum Tg level can predict metastasis in PTC patients after total thyroidectomy. MATERIALS AND METHODS: We enrolled 140 PTC patients in whom serum thyroid-stimulating hormone (TSH) and Tg levels were measured 7 days before radio-iodine (RAI) treatment (TSHA and TgA) and on the day of RAI treatment (TSHB and TgB) with withholding L-thyroxine for 4 weeks before RAI treatment. The values of TSHinc (TSHB-TSHA) and Tginc (TgB-TgA), Tgratio (TgB/TgA), Tginc/TSHinc and Tgratio/TSHinc were calculated. Tginc/TSHinc and Tgratio/TSHinc were tested if those parameters can predict MD in patients with TSHA>30 microIU/mL and TgA<10 ng/mL. RESULTS: Forty-four patients had MD and 96 had no evidence of MD (non-MD). MD group showed higher levels of TgA, TgB, Tginc, Tginc/TSHinc and Tgratio/TSHinc compared with non-MD group. A significant correlation was found between TSHinc and Tgratio (r=0.669) in MD group. In 43 patients with TSHA>30 microIU/mL and TgA<10 ng/mL (MD, 9; non-MD, 34), both Tginc/TSHinc (100%) and Tgratio/TSHinc (89%) had higher sensitivities for predicting MD than TgB (78%). CONCLUSION: With the increment in serum Tg corrected for the increment in serum TSH, serial measurements of off-thyroxine serum TSH and Tg levels can help predict PTC metastasis.