Fifty patients with primary fibromyalgia and a negative cardiovascular symptom history underwent echocardiography to determine the prevalence of mitral valve prolapse (MVP). The mean age of the population was 40 +/- 13 years (14 men, 36 women). Mitral valve prolapse was detected in 75%; 33% with myxomatous mitral valve leaflets. The prevalence of MVP in this population is significantly higher (p less than 0.0001) than in the general population. Primary fibromyalgia and MVP may be part of a more generalized connective tissue abnormality characterized by distinct genetically determined variants.