Background The body's immune-nutrition status affects prognosis in patients with lung cancer. The Controlling Nutritional Status (CONUT) score is an immune-nutrition-related index associated with prognosis in other tumors. We aimed to assess the value of CONUT scores in predicting prognosis in patients with lung cancer. Methods In this retrospective, multicenter study, 1339 patients with lung cancer were divided into low and high CONUT score groups. The relationship between CONUT scores and overall survival (OS) was assessed by survival curves and Cox proportional hazards regression modeling. A nomogram, including CONUT scores and other clinical variables, was established. Results There were 659 (49.2%; mean age, 59.91 years) low and 680 (50.8%; mean age, 62.23 years) high CONUT score patients. OS was significantly worse in patients with high than in those with low CONUT scores (P < 0.001), even after stratification by pathological types (non-small-cell lung cancer and small-cell lung cancer) and Tumor, Node, Metastasis (TNM) stages. A high CONUT score independently predicted risk in patients with lung cancer (adjusted hazard ratio, 1.48; 95% CI, 1.26-1.73; P < 0.001). The CONUT-based nomogram could predict prognosis well (C-index, 0.701), with better resolution and accuracy than TNM staging for predicting OS at 1, 2, and 3 years (area under the receiver operating characteristic curve, 0.735 vs 0.678, 0.742 vs 0.696, and 0.768 vs 0.743, respectively). Conclusion The CONUT score can predict prognosis in patients with lung cancer. A CONUT-based nomogram can improve the accuracy of survival prediction in such patients.