A Markov-based cost-effectiveness model was developed to project long-term effectiveness and costs among patients who undergo nephrectomy for renal cell carcinoma and receive either adjuvant pembrolizumab, adjuvant sunitinib, or routine surveillance alone (no adjuvant treatment). Over a lifetime horizon, pembrolizumab was estimated to prolong quality-adjusted life expectancy and be cost-effective relative to both comparator treatment strategies. Introduction : Pembrolizumab was recently approved as an adjuvant treatment of renal cell carcinoma (RCC), based on prolonged disease-free survival compared to placebo in the phase III KEYNOTE564 trial. The objective of this study was to evaluate the cost-effectiveness of pembrolizumab as monotherapy in the adjuvant treatment of RCC post-nephrectomy, from a US health sector perspective. Patients and Methods : A Markov model with 4 health states (disease-free, locoregional recurrence, distant metastases, and death) was developed to compare the cost and effectiveness of pembrolizumab versus routine surveillance or sunitinib. Transition probabilities were estimated using patient-level KEYNOTE-564 data (cutoff: June 14, 2021), a retrospective study, and published literature. Costs of adjuvant and subsequent treatments, adverse events, disease management, and terminal care were estimated in 2022 US$. Utilities were based on EQ-5D-5L data collected in KEYNOTE564. Outcomes included costs, life-years (LYs), and quality-adjusted LYs (QALYs). Robustness was assessed through one-way and probabilistic sensitivity analyses. Results : Total cost per patient was $549,353 for pembrolizumab, $505,094 for routine surveillance, and $602,065 for sunitinib. Over a lifetime, pembrolizumab provided gains of 0.96 QALYs (1.00 LYs) compared to routine surveillance, yielding an incremental cost-effectiveness ratio of $46,327/QALY. Pembrolizumab dominated sunitinib with 0.89 QALYs (0.91 LYs) gained while saving costs. At a $150,000/QALY threshold, pembrolizumab was cost-effective versus both routine surveillance and sunitinib in 84.2% of probabilistic simulations. Conclusion : Pembrolizumab is projected to be cost-effective as an adjuvant RCC treatment versus routine surveillance or sunitinib based on a typical willingness-to-pay threshold.