Background: Small cell lung cancer (SCLC) is a highly aggressive type of lung cancer with a tendency towards early recurrence and limited survival. Standard-of-care in 1^st-line treatment is platinum-etoposide chemotherapy plus anti-PD-L1 immune checkpoint inhibitor atezolizumab or durvalumab, based on landmark, randomized, phase 3 clinical trials. Methods: IFCT 1905-CLINATEZO is a nationwide, non-interventional, retrospective chart review study of patients (pts) with extensive-stage SCLC who received atezolizumab + chemotherapy as part of the French early access program between May 2019 and January 2020 (1402 pts). Inclusions were exhaustive per participating centers (65/307). Data collection run from February to November 2021. Key objectives were to assess effectiveness and safety of atezolizumab + chemotherapy and analyze subsequent treatment sequences. Results: The population analyzed included 518 out of the 1402 pts. There were 66% male and mean age was 65.7 years (range: 36.7-88.0); 89% had a performance status (PS) 0/1 and 27% brain metastases. Almost all the pts (96%) were smokers, with a median number of pack-years of 40. Fifty-five pts (10.6%) received at least 1 previous treatment. Median number of atezolizumab injections was 7 (range: [1-48] ) for a median duration of 4.9 months (95% CI 4.5-5.1). Twenty-seven pts (5%) were under ongoing treatment at date of last news. Atezolizumab was continued beyond disease progression in 122 pts (24%) for a median duration of 1.9 months (95% CI 1.4-2.3). Best objective response was complete and partial response in 19 (3.9%) and 378 pts (77.1%) respectively; stable disease was observed in 50 pts (10.2%). After a median follow-up of 30.8 months (95% CI: [29.9-31.5]), median overall survival (OS), 12- and 24-months OS rates were 11.3 months (95% CI: [10.1-12.4]), 46.7% (95% CI 42.3-50.9) and 21.2% (95% CI 17.7-24.8) respectively. Median real world-progression free survival (based on date of the first source evidence for progression referenced by the treating physician), 6- and 12-months rates were 5.2 months (95% CI 5.0-5.4), 37.5% (95% CI 33.3-41.7) and 15.2% (95% CI 12.2-18.6) respectively. For the pts with PS 0/1, median OS was 12.2 months (95% CI 11.0-13.5). For the 55 pts with previous treatment, median OS was 14.9 months (95% CI 10.1-21.5). A total of 326 (66.4%) pts received subsequent treatment. Conclusions: IFCT 1905-CLINATEZO study shows the reproducibility, in a real-life setting, of the key survival outcomes of IMpower-133, that may be attributed to the selection of pts fit for this regimen, the adoption of pragmatic approaches for the management of pts receiving atezolizumab, that includes concurrent radiotherapy and treatment beyond progression, and the high proportion of pts treated with 2^nd-line therapies, mostly based on chemotherapy.