Background: Besides the cancer itself, venous thromboembolism (VTE) is the leading cause of death in cancer patients receiving outpatient chemotherapy (CT). Data on VTE development and impact on treatment course and outcome in real-life NSCLC patients receiving immune check-point inhibitors (ICI) is currently sparse. More knowledge within this area is warranted due to the emerging use of ICI in clinical practice. Objectives: To quantify risk of VTE and recurrent VTE in NSCLC patients receiving ICI. Explore the clinical impact of VTE on ICI course and survival and explore potential risk factors for VTE. Patients/methods: Patients with advanced/metastatic NSCLC treated with an immune checkpoint inhibitor (ICI) at the University Hospital of Odense, Denmark during 2015–2018 were identified and data gathered retrospectively from electronic medical records (n = 118). All patients had finished ICI at the time of data-cut off. Baseline Khorana Score (KRS) was calculated within one week prior to ICI initiation. Based on follow-up data cumulative incidence of VTE and its impact on outcome and survival was performed using Kaplan Meier and cox-regression hazard estimation. Results: Risk of VTE was 8% during ICI and 15% at any time point after ICI initiation. Cumulative incidence rates of VTE at 1, 3, 6 and 18 months after first ICI was 1.7%, 5.2%, 6.9% and 13.8% respectively. Median time to VTE during ICI was 2.3 months [IQR 0.6–5.4]. Having VTE during ICI lead to discontinuation of ICI in 78% of cases, most due to fatal PE. History of VTE before onset of ICI was a significant risk factor for recurrent VTE during ICI (24% within this subgroup) despite use of anticoagulant therapy. Conclusions: The incidence and impact of VTE during ICI for real-life NSCLC patients is not negligible with almost 10% developing VTE leading to termination of further ICI in the majority of cases - many due to fatal PE. The risk of recurrent anticoagulant resistant VTE in patients with known VTE during ICI is also considerable, which calls for better management and prevention of VTE including development of treatment specific VTE risk assessment models.