Currently, positron emission tomography with computerized tomography (PET-CT) is the most sensitive technique for detecting extracranial metastases in non-small cell lung cancer (NSCLC). It has been reported that there is a correlation between the maximal standardized uptake value (SUVmax) of primary tumors and prognosis in patients with NSCLC. The effect of sunlight exposure on PET-CT SUVmax value is not known. Therefore, we aimed to evaluate the effect of sunlight exposure on PET-CT SUVmax a value in patients with NSCLC. A total of 290 patients with NSCLC from two different regions of Turkey (Kayseri, n=168 and Adana, n=122) that have different climate and sunlight exposure intensity, were included in the study. Age, gender, histology of cancer, cancer stage, smoking status, comorbidity and SUVmax of the primary tumor area at the time of staging were evaluated as prognostic factors. In the multivariate analysis, we detected that the region was the only independent factor affecting SUVmax (P=0.019). We identified that warmer climate and more sunlight exposure significantly increases the SUVmax value of the primary tumor area in patients with NSCLC. Further studies are warranted to clarify the issue.