Interstitial lung disease (ILD) seems to be associated with an increased risk of lung cancer (LC) and to have a poorer prognosis than LC without ILD. The frequency of ILD in an LC cohort and its prognosis implication need to be better elucidated. This retrospective, observational, cohort study evaluated the frequency of ILD among LC patients (LC-ILD) diagnosed over a 2-year period. LC-ILD patients' characteristics were compared to those with LC without ILD (LC-noILD). Lastly, we conducted a case-control study within this cohort, matching three LC-noILDs to each LC-ILD patient, to evaluate the ILD impact on LC patients' prognoses. Among 906 LC patients, 49 (5.4%) also had ILD. Comparing LC-ILD to LC-noILD patients, respectively, more were men (85.7% vs. 66.2%; = 0.02); adenocarcinomas were less frequent (47.1% vs. 58.7%, = 0.08); median [range] and overall survival was shorter: (9 [range: 0.1-39.4] vs. 17.5 [range: 0.8-50.4] months; = 0.01). Multivariate analysis (hazard ratio [95% confidence interval]) retained two factors independently associated with LC risk of death: ILD (1.79 [1.22-2.62]; = 0.003) and standard-of-care management (0.49 [0.33-0.72]; < 0.001). Approximately 5% of patients with a new LC diagnosis had associated ILD. ILD was a major prognosis factor for LC and should be taken into consideration for LC management. Further studies are needed to determine the best therapeutic strategy for the LC-ILD population.