OBJECTIVES: Episode Grouping is a methodology that enables health care professionals to analyze patient treatments and evaluate the quality of the treatments and manage the related costs. There are three procedures or treatments for a patient with coronary artery disease. Re-blocking an artery after a procedure directly affects the cost and severity of the treatment. We use statistic and probability method to examine the information about patients with coronary artery disease and estimate the risk of re-blocking an artery after each procedure. METHODS: A dataset provided by an insurance company is used. It contained about 6,500,000 patient claims related to year 2000-2005. Data processing is done by using SAS software and SAS codes. Then based on some assumptions and conditional probability the risk of re-blocking an artery after each procedure (bare-stent, drug-eluting stent, and open bypass surgery) are estimated. RESULTS: Comparing the three types of procedures; bypass surgery, drug-eluting stent, and bare stent, shows that the risk of re-blocking an artery after a bare stent is almost 24%, and by using the drug-eluting stent, this risk decreases to almost 13%. Bypass surgery procedure has the lowest re-blocking rate that is less than 7%. CONCLUSIONS: The Drug-eluting stent reduces the rate of re-blocking an artery to 46% compared to the bare stent. This is the main reason for shifting from the bare stent to the drug-eluting stent and makes the drug-eluting stent more effective. But the rate of re-blocking after the drug-eluting stent is still about 6% more than the rate of re-blocking after an open bypass surgery. The main question remaining is how we can estimate the severity and quality of life after each procedure and justify the cost-effectiveness of one of this procedure.