Twenty-seven patients with echocardiographic evidence of primary mitral valve prolapse (MVP) were tested for the presence of joint hypermobility using the criteria of Beighton and Horan. In the examined group, joint hypermobility was found in 14 patients (52%). This occurrence was statistically significant. In patients with simultaneous occurrence of MVP and articular hypermobility we have found a number of pathologic arthrologic manifestations, such as arthralgias, synovitic reactions, distortions, low back pain, and others. In patients with articular hypermobility, there were increased functions of antigen B 35.