The present study was designed to investigate the incidence of benign joint hypermobility syndrome (BJHMS) in mitral valve prolapse (MVP) and the correlation between the echocardiographic features of the mitral valve and elastic properties of the aortic wall and Beighton hypermobility score (BHS) in patients with MVP and BJHMS. Fourty-six patients with nonrheumatic, uncomplicated, and isolated mitral anterior leaflet prolapse (7 men and 39 women, mean age; 26.1 +/- 5.9) and 25 healthy subjects (3 men and 22 women, mean age, 25.4 +/- 4.3) were studied. Patients were divided into two groups according to their BHS (group I, MVP+BJHMS; group II, MVP-BJHMS). Individuals with accompanying cardiac or systemic disease were excluded. Echocardiographic examination was performed in all subjects. The presence of BJHMS was evaluated according to Beighton's criteria. The incidence of BJHMS in patients with MVP was found to be significantly higher than that of controls (45.6%, (21/46) vs 12% (3/25), P < 0.0001). Group I (MVP + BJHMS) had significantly increased anterior mitral leaflet thickness (AMLT, 3.4 +/- 0.4 vs 3.1 +/- 0.3; P < 0.005), maximal leaflet displacement (MLD, 2.4 +/- 0.4 vs 1.7 +/- 0.4; P < 0.005), and degree of mitral regurgitation (DMR, 17.1 +/- 7.2 vs 11.2 +/- 4.4; P < 0.01) compared to group II. However, the index of aortic stiffness (IAOS) was found to be lower (17.6 +/- 6.9 vs 23.9 +/- 7.6; P < 0.005) and aortic distensibility (AOD) to be higher (0.0035 +/- 0.007 vs 0.0024 +/- 0.005; P < 0.005) in group I. There was a significant correlation between AMLT, MLD and DMR, and BHS (r = 0.57/P = 0.007, r = 0.55/P < 0.009, r = 0.51/P < 0.01, respectively). In addition, AOD correlated positively with BHS (r = 0.53/P < 0.005), but the index of aortic stiffness correlated inversely with BHS (r = -0.49/P < 0.007). The incidence of BJHMS in patients with MVP was more frequent than the normal population and there was a significant correlation between the severity of BJHMS (according to BHS) and echocardiographic features of the mitral leaflets and elastic properties of the aortic wall.