Mitral valve prolapse has been recognized as a clinical entity for only the past 50 years, although the auscultatory findings of this condition had been recognized since the mid-19th century. On the evidence of only a few autopsies, it was concluded that the basis for these were pleuropericardial adhesions. Left ventricular angiographic studies performed in the 1960s clearly documented the true nature of the condition, although it was not until the advent of echocardiography that large numbers of patients began to be referred for evaluation by this new technique. Because of the wide variety of symptoms in patients with suspected mitral valve prolapse, similar to those with other conditions, many patients with the latter were referred for evaluation and diagnosed with mitral valve prolapse because of misleading M-mode and then 2-dimensional criteria. It is now recognized, with the use of improved, more restrictive echocardiographic criteria, that the prevalence of the disorder is much less than previously believed. No test has been devised that will prove 100% sensitive and 100% specific for any disorder. In conclusion, this sobering fact should encourage the use of all modalities available, including clinical skills, to make proper diagnoses when these may be in doubt.