Background: Patients with surgically resected EGFR+ NSCLC remain at risk of recurrence after surgery. Osimertinib, a tyrosine kinase inhibitor, had been assessed clinically as adjunctive therapy in surgically resected EGFR+ NSCLC including stage 3A. We conducted a cost effectiveness/utility analysis of adjunctive osimertinib therapy in stage 3A surgically resected EGFR+ NSCLC. Methods: We specified a two state partitioned survival model of disease free survival (DFS) versus disease recurrence and death in a), with a 5 year time horizon (US payer perspective). DFS and overall survival curves were extrapolated per parametric functions. A 3% discount rate was utilized to costs and utilities beyond year 1. Costs of therapies (wholesale acquisition cost), adverse events (AE; grade 3/4; all grades for immunotherapy related AEs), and monitoring costs were based on Redbook, publications, and Physician Fee Schedules, respectively (US $2021). Costs, DFS life years (DFSLY) and DFS quality adjusted life years (DFSQALY) were used to determine the incremental cost effectiveness/utility ratios (ICER/ICUR) of the additional cost needed to gain (g) a DFSLY and DFSQALY in base case (BSA) and probabilistic sensitivity analyses (PSA). Results: Exponential regression was used to extrapolate the Kaplan-Meier curves of osimertinib and placebo,. As shown in the table, the BCA (PSA) estimated the incremental cost at $669,369 ($670,274). The incremental DFSLY was 1.895 (1.899), yielding ICER of $353,125/DFSLYg ($352,963/DFSLYg). The incremental DFS QALY was 1.35, yielding an ICUR of $497,905/DFSQALYg ($497,676/DFSQALYg). Conclusions: In stage 3A surgically resected EGFR+ NSCLC, adjunctive osimertinib therapy showed incremental benefits of 1.895 (1.899) DSFLYg and 1.344 (1.349) QALYg compared to placebo, however at marked incremental cost. As adjunctive osimertinib treatment is indicated in EGFR+ NSCLC disease stages1B and 2, the present stage 3A cost effectiveness/utility results should be compared to those for stages 1B and 2.