Background: Up to 10% of patients with advanced non-small cell lung cancer (aNSCLC) have pre-existing interstitial lung disease (ILD). These patients are usually excluded from immunotherapy clinical trials. Consequently, knowledge on outcomes following nivolumab treatment in these patients remains limited. The primary objective of this study was to evaluate survival outcome following nivolumab treatment in ILD patients with pre-treated aNSCLC in the real-world setting. Patients and methods: The study included all patients with aNSCLC recorded in the French hospital database, starting nivolumab in 2015–2016. Patients were stratified by pre-existing ILD and three subgroups were studied [auto-immune or granulomatous (AI/G) ILD, other known causes ILD and idiopathic ILD]. Time to discontinuation of nivolumab treatment [time to treatment duration (TTD)] and overall survival (OS) were estimated using Kaplan–Meier survival analysis. Results: Of 10,452 aNSCLC patients initiating nivolumab, 148 (1.4%) had pre-existing ILD. Mean age at nivolumab initiation was 64.6 ± 9.4 years in ILD and 63.8 ± 9.6 years in non-ILD. Compared to non-ILD, patients in the ILD group were more frequently men ( p < 0.05) and had more comorbidities ( p < 0.001). There was no significant difference between ILD and non-ILD groups for median TTD (2.5 versus 2.8 months; p = 0.6) or median OS (9.6 versus 11.9 months; p = 0.1). Median OS in AI/G ILD ( n = 14), other known causes ILD ( n = 75), and idiopathic ILD ( n = 59) were 8.6, 10.7, and 9.6 months, respectively. Conclusion: In this large cohort of aNSCLC patients with ILD, outcomes are similar to those obtained in the non-ILD population. Immunotherapy could be beneficial for these patients.