Purpose: To assess prospectively the accuracy of phase-contrast cine MR angiography in the detection of thoracic aortic dissection with operative correlation. Materials and methods: One hundred and ninety-seven symptomatic patients suspected of having thoracic aortic dissection or aneurysm as well as 13 patients suspected of having thoracic aortic coarctation and 20 asymptomatic normals (as controls) were examined prospectively with phase-contrast cine MR angiography on a 1.5-T MR imager. Seventy-eight of these patients had operative correlation, and only these 78 patients were included in the statistical analysis. Results: There were 51 true positive and 27 true negative findings of thoracic aortic dissection in this study for an accuracy of 100%. Conclusion: Phase-contrast cine MR angiography is an accurate non-invasive imaging technique for evaluating patients suspected of having thoracic aortic dissection.