Objective Prolapse of mitral valve leaflets is a frequent disorder and the most common cause of severe mitral regurgitation in western countries. However, little is known about the effects of altitude on mitral valve prolapse. We studied the prevalence and echocardiographic characteristics of mitral valve prolapse at moderately high altitude and sea level. Methods A total of 936 consecutive subjects who were admitted to 2 study institutions at Kars, Turkey (1750 m) and Istanbul, Turkey (7 m) were enrolled in this study to determine prevalence of mitral valve prolapse. Demographic and 2-dimensional echocardiographic characteristics of participants were recorded. Results Prevalance of mitral valve prolapse was found to be significantly higher in people living at moderate altitude compared with those living at sea level (6.2% vs 2.0%; P = .007). Overall echocardiographic features regarding valve thickness (4.1 ± 0.80 mm vs 3.6 ± 0.66 mm; P = 0.169), maximal valve prolapse (4.6 ± 2.08 mm vs 3.9 ± 0.91 mm; P = .093), and frequency of mitral regurgitation (89% vs 73%; P = .65) were similar between groups, although anterior valve prolapse was seen more frequently at moderate altitude (50% vs 11%; P = .056) and posterior leaflet prolapse was significantly more frequent at sea level (66% vs 10%; P = .002). Conclusions Mitral valve prolapse is more frequently observed at moderately high altitudes. Further studies are needed to determine clinical importance of our findings.