['We assessed the clinical profile of patients with acute coronary syndrome (ACS) and nonobstructive coronary artery disease (CAD) in a real world setting, focusing on pattern of care and on prognosis.', 'Each nonobstructive CAD (<50% stenosis in any epicardial coronary artery) patient was matched with an obstructive CAD patient; adjusted estimates of prescription of guideline-recommended drugs at discharge and of long-term prognosis were evaluated.', 'Among 2995 consecutive ACS patients who underwent coronary angiography, 125 (4.2%) had nonobstructive CAD. Nonobstructive CAD patients had significantly lower odds of receiving aspirin [odds ratio (OR) 0.31, 95% confidence interval (CI): 0.14-0.68], thienopyridines (OR 0.01, 95% CI: 0.00-0.07), statins (OR 0.31, 95% CI: 0.17-0.58), beta-blockers (OR 0.32, 95% CI: 0.17-0.63) and angiotensin converting enzyme-inhibitors /angiotensin receptor blockers (OR 0.36, 95% CI: 0.17-0.91) compared with matched patients. During a 3-year follow-up, nonobstructive CAD patients had significantly fewer cardiovascular deaths and myocardial infarctions but numerically more episodes of unstable angina.'] Are patients with acute coronary syndrome and nonobstructive coronary artery disease in the real world markedly undertreated?