Background: Patients with stage 1B non-small cell lung cancer (NSCLC) who receive surgical resection are at continued risk of disease recurrence and death after the surgery. Osimertinib, a tyrosine kinase inhibitor indicated for epidermal growth factor receptor positive (EGFR+) NSCLC, has been used post-operatively as adjunctive therapy to improve clinical outcomes in surgically resected EGFR+ stage 1B NSCLC. We evaluated the cost effectiveness/utility of adjunctive osimertinib treatment post-surgically in stage 1B. Methods: A two state partitioned survival model with disease free survival (DFS) and disease recurrence or death was specified (US payer perspective). Kaplan-Meier DFS curves were fitted to parametric functions. A 5 year time horizon was adopted and a 3% discount rate was applied to costs and utilities after year 1. Wholesale acquisition costs for treatments were sourced from Redbook, adverse event costs (grade 3/4; all grades for immunotherapy related AEs) utilized published data, and monitoring costs were based on Physician Fee Schedules (US $2021). We estimated incremental costs, DFS life years (DFSLY), and DFS quality adjusted life years (DFSQALY). Based on DFSLY and DFSQALY gained (g), incremental cost effectiveness/utility ratios (ICER/ICUR) were determined in base case analyses (BCA) and probabilistic sensitivity analyses (PSA). Results: Exponential regression was utilized to extrapolate the osimertinib DFS Kaplan-Meier curve, while Weibull regression was applied for extrapolation of the placebo DFS curve. Shown in the table below, the BCA (PSA) revealed incremental cost of $774,710 ($775,941) and ncremental DFSLY of 0.813 (0.954), yielding an ICER of $952,797/DFSLYg ($813,162/DFSLYg); and incremental DFSQALY of 0.576 (0.676), yielding an ICUR of $1,345,340/DFSQALYg (1,147,793/DFSQALYg). Conclusions: In surgically resected stage 1B EGFR+ NSCLC, the model estimated incremental benefits of 0.813 (0.954) LYg and 0.576 (0.676) QALYg, however at marked incremental cost. As adjunctive osimertinib treatment is indicated in EGFR+ NSCLC disease stages 2 and 3A, the present stage 1B cost effectiveness/utility results should be compared to those for stages 2 and 3A.