Isolated mitral valve prolapse (MVP) may represent one end of a spectrum of disease involving dysfunction of multiple cardiac valves. Eighty-nine consecutive patients with MVP diagnosed by two-dimensional echocardiography (2-D echo) were prospectively studied specifically to determine the incidence of tricuspid valve prolapse (TVP) and its clinical correlations. Criteria for prolapse of the atrioventricular (A-V) valves by 2-D echo included extension of the valve leaflets behind an imaginary line defining the valve annulus. Forty-one of 82 patients with MVP had associated TVP. No significant differences existed between patients with isolated MVP and combined A-V valve prolapse with regard to sex, clinical history, symptoms, or physical examination. The parasternal long axis view was more sensitive than the apical four chamber view in diagnosing prolapse of either mitral or tricuspid valves. Thus, TVP is a frequent concomitant of MVP and occurs with equal frequency in both young and old patients.