Background: A minority of the approximately 40,000 US patients diagnosed annually with stage III NSCLC can be cured by concurrent CRT. Standard adjuvant immune checkpoint inhibitors (ICI) improve outcome for those patients who complete CRT with good performance status (PS) and without disease progression, but most patients diagnosed with unresectable stage III NSCLC will not meet the criteria for adjuvant ICI. AFT-16 investigated safety and efficacy of neoadjuvant and adjuvant atezolizumab as a strategy that may allow more patients to benefit from ICI. Methods: Eligible patients received 4 cycles (cy) of atezolizumab 1200 mg IV q 21 days followed by CRT with 60 Gy + weekly carboplatin and paclitaxel (CP), CP consolidation and adjuvant atezolizumab to complete 1 year of therapy (17 cy). The primary endpoint of disease control rate at 12 weeks (wks) has been reported. Secondary endpoints reported here include overall response rate, safety, and progression-free and overall survival (PFS, OS) measured from the start of induction therapy. Correlative science data and quality of life endpoints will be reported elsewhere. Results: 64 patients with unresectable stage III NSCLC, PS 0-1 and no active autoimmune disease or significant organ dysfunction were enrolled at 13 Alliance for Clinical Trials in Oncology sites from 11/2017 to 7/2019. 62 patients who received at least one dose of atezolizumab are included in this analysis. Median age was 63.9 years (range 38.1-86.5). Patients were 51.6% female, 77.4% white, 88.7% current & former smokers and 56.5% PS 0. All patients are off study treatment. Mean cycles of treatment received was 9 (1-17). 46 patients were alive at median follow up 24.1 mo (range 3 – 34.1 mo). PFS at 12 and 18 mo from start of induction atezolizumab was 66% (95%CI 55-79) and 57% (95%CI 45-71) respectively. Median PFS was 23.7 mo (95%CI 13.2-NE). OS at 18 mo was 84% (95%CI 75-94). Median OS is not yet estimable. Atezolizumab was well tolerated. One grade (gr) 4 Guillain-Barre syndrome and 1 each gr 3 pneumonia, pneumonitis and colitis were attributable to neoadjuvant atezolizumab. The remaining 9 severe adverse events were unrelated to ICI. Conclusions: Atezolizumab prior to and following CRT for stage III unresectable NSCLC was well tolerated with encouraging PFS and OS without unexpected safety signals. Analysis of correlative endpoints and quality of life are ongoing. Further study of induction atezolizumab is warranted in patients with unresectable stage III NSCLC. Support: https://acknowledgments.alliancefound.org; Clinical trial information: NCT03102242