Background: Pembrolizumab 400 mg every six weeks (Q6W) and nivolumab 480 mg every four weeks (Q4W) are used since 2020 and the coronavirus disease 2019 (COVID-19) pandemic. This recommendation relied on pharmacokinetic and pharmacodynamic models. The objective of the IDEE (Immunothérapie Double dose Etendue: Experience bretonne) study is to determine the safety and efficacy of this treatment regimen in real life conditions. Methods: We conducted an observational, retrospective, multicentric study including 117 patients with advanced non-small cell lung cancer (NSCLC) who received pembrolizumab Q6W or nivolumab Q4W between March 2020 and March 2021. Results: The median age was 67 years, 68% were men with predominantly lung adenocarcinoma. The median time to double-dose regimen failure (TDDF) was 9.2 months. The survival rate at 12 months was 79%. TDDF was not influenced by sex, line of treatment, pathologic subtypes or anti-programmed cell death protein 1 (PD-1) antibody. There was no correlation between TDDF and duration of prior exposition to immunotherapy before switching. Sixty-eight patients experienced double-dose treatment failure, 28% because of toxicity including five definitive discontinuations. Five grade ≥3 immune-adverse events were reported included two cases of pneumonitis, all responding to corticosteroid therapy. Conclusions: Our multicentric cohort supports the feasibility of pembrolizumab Q6W and nivolumab Q4W for patients with advanced NSCLC. There is no warning signal regarding safety neither efficacy in our real-life data.