A valve ring abscess was diagnosed in four patients with a prosthetic aortic valve by identifying an echo-free space on two-dimensional echocardiography. Three of the patients presented with severe aortic regurgitation and congestive heart failure after an episode of endocarditis, but two of them did not have evidence of active endocarditis. The fourth patient had endocarditis, but no evidence of aortic regurgitation or heart failure. All four patients required valve replacement. Similar findings in all 11 previously reported cases suggest that a valve ring abscess can be diagnosed by two-dimensional echocardiography. It may be found without clinical evidence of endocarditis, in the absence of aortic regurgitation, without echocardiographically identifiable vegetations or during resolution of endocarditis.