BACKGROUND: The impact of insurance coverage on the care of patients with non-ST-segment elevation acute coronary syndromes (NSTE ACS) is unclear. OBJECTIVE: To compare NSTE ACS care patterns by insurance type. DESIGN: Comparison of Medicaid patients younger than 65 years of age and Medicare patients 65 years of age or older with patients of similar age who have health maintenance organization (HMO) or private insurance coverage. SETTING: 521 U.S. hospitals participating in the CRUSADE (Can Rapid Risk Stratification of Unstable Angina Patients Suppress ADverse Outcomes with Early Implementation of the ACC [American College of Cardiology]/AHA [American Heart Association] Guidelines) quality improvement initiative from January 2001 through March 2005. PATIENTS: 37,345 NSTE ACS patients younger than 65 years of age and 59,550 patients 65 years of age or older. MEASUREMENTS: Guideline-recommended treatments, and in-hospital outcomes. RESULTS: Medicaid was the primary payer for 18.7% (6999 of 37,345) of patients younger than age 65 years, whereas Medicare was the primary payer for 67.5% (40,199 of 59,550) of patients age 65 years or older. Medicaid patients were statistically significantly less likely to receive short-term (less than 24 hours) medications and to undergo invasive cardiac procedures than patients covered by HMO and private insurance. They also had higher mortality rates (2.9% vs. 1.2%; adjusted odds ratio, 1.33; 95% CI, 1.08 to 1.63). Medications and invasive procedures were used to a similar extent in patients with Medicare and HMO or private insurance, and respective mortality rates were not significantly different (6.2% vs. 5.6%; adjusted odds ratio, 1.08; 95% CI, 0.99 to 1.18). LIMITATIONS: Self-pay patients and patients without insurance were not assessed. CONCLUSIONS: NSTE ACS patients with Medicaid (but not Medicare) as the primary payer were less likely to receive evidence-based therapies and had worse outcomes than patients with HMO or private insurance as the primary payer. The causes of these treatment differences and solutions for narrowing the gaps in quality require further investigation.