Benign hypermobility as defined by a modification of the Carter-Wilkinson criteria was found in 31 of 637 healthy blood donors, a prevalence of 5%. No increased prevalence of arthritis/arthralgia or characteristics suggestive of Ehlers-Danlos syndrome other than a possible familial predisposition were found when these 31 hypermobile subjects were compared to an age and sex matched two-for-one control group. Cardiac evaluation by auscultation, electrocardiogram, and echocardiogram showed no increased occurrence of mitral valve prolapse in hypermobile subjects. Thus the benign hypermobile joint syndrome appears to be one extreme of the range of normal joint motion and not a systemic connective tissue disorder.