To date, the relation between mitral stenosis (MS) and other associated cardiac valvular lesions has been reported by angiography and surgical pathologic study in patients with more advanced disease but has not been studied systematically by two-dimensional echocardiography and Doppler color flow mapping in a large referral population with a broader spectrum of severity. In addition, prior reports have suggested that up to 40% of patients with MS have mitral valve prolapse (MVP); however, because of recent developments in two-dimensional echocardiographic imaging and the definition of MVP, this association must now be reconsidered. The purpose of this study was to explore the association of other valvular lesions with MS and their relation to its severity and in particular to test whether MS is in fact associated with MVP with the frequency reported previously. We reviewed the studies of 205 consecutive patients (aged 61 +/- 14 years; range 26 to 87 years) with MS who were studied from 1992 to 1994 by two-dimensional echocardiography and Doppler color flow mapping to assess valvular stenosis, regurgitation, and MVP in patients with a range of severity of MS (28% mild, 34% moderate, and 38% severe MS based on mitral valve area). MS was associated with at least mild mitral regurgitation in 78% of patients (160/205), and pure MS was correspondingly uncommon (22%). There was an inverse relationship between the severity of MS and the degree of mitral regurgitation (p < 0.001). MS was frequently associated (54% of patients) with significant lesions of other valves, including aortic stenosis (17%), at least moderate aortic regurgitation (8%) and tricuspid regurgitation (38%), and tricuspid stenosis (4%). Tricuspid stenosis was associated with more severe MS (p < 0.01), and tricuspid regurgitation was more common in patients with mixed MS and regurgitation than in those with pure stenosis (60% versus 26% for at least moderate tricuspid regurgitation; p < 0.001). Mitral valve prolapse was present in only one patient (0.5%). Superior systolic bulging of the midportion of the anterior mitral leaflet toward the left atrium (but not superior to the annular hinge points) was seen in 22 patients (11%). Patients with such superior bulging had significantly lower mitral valve scores but a similar degree of mitral regurgitation compared with those without bulging. The majority of patients with MS (78%) have associated mitral regurgitation and significant lesions of the other cardiac valves (54%). The frequency of true MVP associated with chronic MS is much lower than reported previously. This may provide insight into the underlying pathophysiologic process, tending to shorten the chordae tendineae and leaflets to produce stenosis rather than elongate them to produce prolapse.