The study deals with the incidence and clinical significance of mitral valve prolapse in the population of outpatient pediatric cardiology patients in the time period from November 1999 to April 2004. The sample included 1187 children of both sexes, 688 of whom had a structural cardiac anomaly (57.9%), and the prolapse was diagnosed in 51 children (4.3%), largely female (f:m = 7.5:1). The average age at establishing diagnosis was 12.4 +/- 2.9 years (range 6-19 years). The children were followed 3.1 +/- 0.9 years (1-4 years of age). In 25 children (49%) associated mitral valve insufficiency was found, mostly of the 1st degree (80%). During follow up, neither the progression of the insufficiency nor any other complication was observed (arrhytmia, tromboembolism) in any of the children. Dolichostenomely was found in 10 children (19.6%), and both the development of insufficiency (p = 0.464, df = 2, chi2 = 1.54) and the difference in constitution (p = 0.766, df = 4, chi2 = 1.83) were irrelevant of sex. Typical subjective symptoms were observed in 37 children (72.5%), 22 of whom were treated with beta-blockers (propranolol) (43.1%). The average age of the patients treated with 3-blockers (13.7 +/- 2.5 yr) was statistically different from the average age of untreated patients (11.5 +/- 2.9 yr), hence the probability of the influence of neurohormonal factors on the development of subjective symptoms in advanced puberty (p = 0.006, t = -2.86). The most common clinical symptom is chest-pain (95% of the group with stronger symptoms). When treated, the symptoms disappear in 82% of the patients. Mitral valve prolapse is the entity of favourable clinical course. The prophylaxis of infective endocarditis should be performed in the group with mitral insufficiency, and the children with stronger symptoms should be treated with beta-blockers.