Context: TK1 found to be elevated biomarker in many solid cancers. Objectives: The study aimed to assess the prognostic significance of a serum TK1 in patients with metastatic NSCLC. Methods: The study included 48 consecutive patients, newly diagnosed with metastatic NSCLC, and 10 healthy volunteers. Serum TK1 activity determined by ELISA method. Results: Patients with a bTK1 level >156 Du L(-1) had significantly shorter survival. TK1 level showed a strong correlation with primary tumor SUV(max). Discussion and conclusion: The magnitude of maximum fluorodeoxyglucose uptake in primary tumors and the serum TK1 level in patients with metastatic NSCLC were found to be independent prognostic predictors of overall survival.