BACKGROUND While occasional reports of mitral valve chordal rupture have been described in hypertrophic cardiomyopathy, the exact prevalence and characteristics of this event in a large medical cohort have not been reported. OBJECTIVE To assess the prevalence of mitral valve chordal rupture in hypertrophic cardiomyopathy and the clinical, echocardiographic, surgical and histological profiles of those patients. METHODS We searched for patients with mitral valve chordal rupture diagnosed by echocardiography among all electronic files of patients admitted to our centre for hypertrophic cardiomyopathy between 2000 and 2010. RESULTS Among 580 patients admitted for hypertrophic cardiomyopathy, six patients (1%, 5 men, age 68-71 years) presented with mitral valve chordal rupture, symptomatic in five cases, always involving the posterior mitral leaflet. In all cases, echocardiography before rupture showed mitral valve systolic anterior motion, with anterior (and not posterior) leaflet elongation compared with a random sample of patients with non-obstructive hypertrophic cardiomyopathy (P=0.006) (and similar to that observed in obstructive hypertrophic cardiomyopathy). Significant resting left ventricular outflow tract obstruction was always present before rupture and disappeared after rupture in the five cases requiring mitral valve surgery for severe mitral regurgitation. Histological findings were consistent with extensive myxomatous degeneration in all cases. CONCLUSIONS Mitral valve chordal rupture is: infrequent in hypertrophic cardiomyopathy; occurs in aged patients with obstructive disease; involves, essentially, the posterior mitral leaflet; and causes, in general, severe mitral regurgitation requiring surgery. Myxomatous degeneration may be the substrate for rupture in these patients.