Purpose: We studied the patterns of FDG uptake of primary papillary thyroid microcarcinoma (PTMCa) lesions and benign thyroid nodules in dual time point 18F-FDG PET/CT imaging. Materials and Methods: Consecutive 134 patients (154 lesions) with PTMCa and 49 patients (61 nodules) with benign thyroid nodules equal to or less than 1.0 cm who underwent dual time point 18F-FDG PET/CT study before surgery were enrolled. We calculated the maximum standardized uptake value of PTMCa and benign nodules in both time points, and percent change of SUVmax (Δ%SUVmax) and lesion to background ratio of SUVmax (Δ%L:B ratio) between both time points. The mean time interval between scans was 23.4±4.4 minutes (thyroid to thyroid interval: 10.7±4.4 minutes). Results: The mean of SUVmax of PTMCa was increased from 4.9±4.3 to 5.3±4.7 (p<0.001) and Δ%SUVmax was 12.3±23.6%. But, the mean of SUVmax of benign nodules was no definite change (2.1±1.0 to 2.1±1.3, p=0.686) and Δ%SUVmax was -0.3±20.5%. Of the 154 PTMCa, 100 nodules (64.9%) showed an increase in SUVmax over time, while 19 (31.1%) of the 61 benign thyroid nodules showed an increase (p<0.001). The dual time point 18F-FDG PET/CT found more PTMCa in visual assessment (62.3% vs. 76.6%, p=0.006), even in smaller than 0.5 cm (38.6% vs. 60.0%, p=0.011). Conclusion: Dual time time 18F-FDG PET/CT imaging was more useful than single time point 18F-FDG PET/CT imaging for distinction between PTMCa and benign nodule, especially when nodule showed equivocal or negative findings in single time point 18F-FDG PET/CT imaging or was smaller than 0.5 cm.