Few studies quantitate the cost of a quality well being as produced by arthroplasty surgery. The objective was to use the Quality of Well Being Index to calculate the cost per quality of well year in knee arthroplasty surgery. The difference in Quality of Well Being Index scores before and after the intervention was calculated and multiplied by the patient's life expectancy. The procedure cost was divided by this quantity resulting in the cost of a quality well year. One hundred patients underwent a primary knee arthroplasty. There were 30 males (average age, 62 years old) and 70 females (average age, 64 years old). The calculated costs per a quality well year were $30,695 (standard deviation $90,883) at 3 months, $17,804 (standard deviation $25,888) at 6 months, $11,560 (standard deviation $11,874) at 1 year, and $6656 (standard deviation $3567) at 2 years postsurgery. Health economists consider an intervention costing less than $30,000 per quality of well year a bargain to society. Cost effectiveness of knee arthroplasty surgery compares favorably with other surgical interventions such as coronary artery bypass surgery ($5000 per quality of well year) and extremely favorable with medical treatments such as renal dialysis ($50,000.00 for the quality well year). Knee arthroplasty is a cost effective procedure and should be considered an appropriate investment by society.