IMPORTANCE: Because of the similarity in clinical outcomes after elective open and endovascular repair of abdominal aortic aneurysm (AAA), cost may be an important factor in choosing a procedure. OBJECTIVE: To compare total and AAA-related use of health care services, costs, and cost-effectiveness between groups randomized to open or endovascular repair. DESIGN, SETTING, AND PARTICIPANTS: This unblinded randomized clinical trial enrolled 881 patients undergoing planned elective repair of AAA who were candidates for open and endovascular repair procedures. Patients were randomized from October 15, 2002, to April 15, 2008, at 42 Veterans Affairs medical centers. Follow-up was completed on October 15, 2011, and data were analyzed from April 15, 2013, to April 15, 2016, based on intention to treat. MAINOUTCOMES ANDMEASURES: Mean total and AAA-related health care cost per life-year and per quality-adjusted life-year (QALY). RESULTS: A total of 881 patients (876 men [99.4%]; 5 women [0.6%]; mean [SD] age, 70 [7.8] years) were included in the analysis. After a mean of 5.2 years of follow-up, mean life-years were 4.89in the endovascular group and 4.84 in the open repair group (P =.68), and mean QALYs were 3.72 in the endovascular group and 3.70 in the open repair group (P =.82). Total mean health care costs did not differ significantly between the 2 groups (endovascular group, $142 745; open repair group, $153 533; difference, -$10 788; 95% CI, -$29 796 to $5825; P =.25). Costs related to AAA, including the initial repair, constituted nearly 40% of total costs and did not differ significantly between the 2 groups (endovascular group, $57 501; open repair group, $57 893; difference, -$393; 95% CI, -$12 071 to $7928; P =.94). Lower costs due to shorter hospitalization for initial endovascular repair were offset by increased costs from AAA-related secondary procedures and imaging studies. The probability of endovascular repair being less costly and more effective was 56.8% when effectiveness was measured in life-years and 55.4% when effectiveness was measured in QALYs for total costs and 31.3% and 34.3%, respectively, for AAA-related costs. CONCLUSIONS AND RELEVANCE: In this multicenter randomized clinical trial with follow-up to 9 years, survival, quality of life, costs, and cost-effectiveness did not differ between elective open and endovascular repair of AAA.