Familial prevalence of mitral valve prolapse in a Chinese population was determined in 22 propositi of whom 10 had straight back (group A), three had abnormally high metacarpal index (group B), and nine had neither (group C). Of 71 (32 male and 39 female subjects) first degree relatives screened, mitral valve prolapse was found in 19 (seven male and 12 female subjects) (26.8%). The familial prevalence among groups A, B, and C was 20%, 30%, and 38.5%, respectively. Our study indicates that the familial occurrence of mitral valve prolapse does not depend on its association with the straight back syndrome.