Limited data exist on the optimal duration of immunotherapy, including for non-small-cell lung cancer (NSCLC). We present an exploratory analysis of CheckMate 153, a largely community-based phase IIIb/IV study, to evaluate the impact of 1-year fixed-duration versus continuous therapy on the efficacy and safety of nivolumab.Patients with previously treated advanced NSCLC received nivolumab monotherapy (3 mg/kg every 2 weeks). Those still receiving treatment at 1 year, including patients perceived to be deriving benefit despite radiographic progression, were randomly assigned to continue nivolumab until disease progression or unacceptable toxicity or to stop nivolumab with the option of on-study retreatment after disease progression (1-year fixed duration).Of 1,428 patients treated, 252 were randomly assigned to continuous (n = 127) or 1-year fixed-duration (n = 125) treatment (intent-to-treat [ITT] population). Of these, 89 and 85 patients in the continuous and 1-year fixed-duration arms, respectively, had not progressed (progression-free survival [PFS] population). With minimum post-random assignment follow-up of 13.5 months, median PFS was longer with continuous versus 1-year fixed-duration treatment (PFS population: 24.7 months v 9.4 months; hazard ratio [HR], 0.56 [95% CI, 0.37 to 0.84]). Median overall survival from random assignment was longer with continuous versus 1-year fixed-duration treatment in the PFS (not reached v 32.5 months; HR, 0.61 [95% CI, 0.37 to 0.99]) and ITT (not reached v 28.8 months; HR, 0.62 [95% CI, 0.42 to 0.92]) populations. Few new-onset treatment-related adverse events occurred. No new safety signals were identified.To our knowledge, these findings from an exploratory analysis represent the first randomized data on continuous versus fixed-duration immunotherapy in previously treated advanced NSCLC and suggest that continuing nivolumab beyond 1 year improves outcomes.