['To investigate the prognostic value of weight loss before diagnosis in patients with advanced stage non-small cell lung cancer (NSCLC) treated with first-line chemotherapy.', 'A total of 81 NSCLC patients with stages IIIB/IV were included in this retrospective cross-sectional study. Study variables were weight loss in the last 3 months before diagnosis, patient demographic, clinical and laboratory characteristics and histological features of the tumor before administering first-line chemotherapy. Then, the patients were stratified into 4 groups based on their weight loss before being diagnosed with NSCLC.', 'The patients were predominantly male (68%), with a smoking history (62%), 5 to 10 kg weight loss in the last 3 months (31%), and had metastatic disease (64%) and adenocarcinoma (40%) at the time of diagnosis. On the other hand, most of the patients with 5 to 10 kg weight loss in the last 3 months before diagnosis had squamous cell carcinoma (44%), stage IV disease (56%), and the first disease progression was in the brain (64%). Pre-diagnosis weight loss had a negative impact on progression-free survival (PFS), independent from weight loss during first-line chemotherapy, but no such effect was noticed on overall survival (OS).'] Is weight loss at the time of diagnosis associated with prognosis in patients with advanced-stage non-small cell lung cancer?