A series of 24 cases of paraprosthetic valvular regurgitation, 10 mitral and 14 aortic, in 19 out of a group of 634 operated patients with a total of 822 prosthetic heart valves is reported. The presenting features are dominated by auscultatory changes, though inconstant episodes of heart failure, and, in aortic prostheses, the high incidence of infective endocarditis. Paraclinical investigations are of variable value; cineradiography in aortic valves and phonocardiography in mitral valves are useful; catheterisation with ventriculography or aortic angiography according to the case under study are the investigations of choice, especially in mitral regurgitation where it is essential. Typical clinical settings for these problems are valve ring dilatation calcification, and previous or active infective endocarditis. The indications for urgent surgery depend on the clinical signs, the presence of heart failure, haemolysis, active endocarditis and deterioration despite medical treatment. The series compares the data in mitral paraprosthetic regurgitation, difficult to diagnose but with a reasonably good prognosis, and aortic paraprosthetic regurgitation, easier to diagnose but associated with a poor prognosis due to the high incidence of associated endocarditis.