To assess the ability of biplane cineangiography in the diagnostic evaluation of acute dissection of the aorta, 20 patients with acute dissection were studied within 24 hours of surgery or autopsy, or both. Biplane large film aortic angiography was performed in 11 patients (Group I) and biplane aortic cineangiography in 9 (Group II). The morphology of the aortic valve was defined precisely in 5 (50 percent) of 10 patients in Group I and in all 9 patients (100 percent) in Group II (p < 0.02). Aortic regurgitation was diagnosed in all patients in both groups in whom it was present (p = not significant). Intimai tears were localized in 5 (50 percent) of 10 patients in Group I and in 8 (89 percent) of 9 in Group II (p < 0.07). Intimal flaps were not identified angiographically in three patients in Group I and were identified in four patients (100 percent) in Group II (p < 0.01). The presence of retrograde dissection was established in three (38 percent) of eight patients in Group I and in four (100 percent) of four patients in Group II (p < 0.05). There was no difference in the ability to identify a nonclotted false lumen between cine and large film angiography. It is concluded that in addition to improved diagnostic capabilities, technical advantages make cineangiography a good alternative to large film angiography in the diagnostic evaluation of patients with acute dissection of the aorta. © 1981.