The prognostic importance of F-18-fluorodeoxyglucose avidity in primary thyroid tumor and molecular basis responsible for its mechanism has not yet been well characterized. In this study, we aimed to evaluate the correlation between the maximum standardized uptake levels and B-type Raf kinase mutation positivity in incidentally detected papillary thyroid cancer patients during F-18-fluorodeoxyglucose positron emission tomography examination. We retrospectively evaluated 6873 F-18-fluorodeoxyglucose-positron emission tomography scans of consecutive subjects from a database search for tumor staging in 2014 at our hospital Nuclear Medicine Center. In total, 135 patients had focal F-18-fluorodeoxyglucose uptake in the thyroid. Of these, 76 patients had fine-needle aspiration biopsy. F-18-fluorodeoxyglucose-maximum standardized uptake of the positron emission tomography-detected nodules was recorded. B-type Raf kinase (V600E) mutation and p53 protein expression were evaluated in papillary thyroid cancer patients. The incidence of thyroid incidentaloma in F-18-fluorodeoxyglucose-maximum standardized uptake scans was 2% (135/6873). Of the 76 patients evaluated, 41% (n = 31) were diagnosed papillary thyroid cancer. B-type Raf kinase mutation was positive in 51% (17/30) of the papillary thyroid cancer patients. Maximum standardized uptake levels of the nodules (>= 1 cm) were significantly higher in Btype Raf kinase-mutated papillary thyroid cancer patients than in non-mutated patients [16.6 (10.4-27.9) vs. 9.7 (6.8-11.1); P = 0.007]. Correlation analysis revealed that maximum standardized uptake was significantly associated with B-type Raf kinase mutation positivity (r = 0.519; P = 0.005). Logistic regression analysis showed an association between maximum standardized uptake and B-type Raf kinase mutation positivity even after adjustment for age and gender (P = 0.01). B-type Raf kinase mutation is closely related to F-18-fluorodeoxyglucose-positron emission tomography maximum standardized uptake levels in patients with incidentally detected papillary thyroid cancer.