Hypertrophic cardiomyopathy (HCM) is a hereditary disease characterised by primary hypertrophy of the left and/or right ventricle. The reference standard for imaging diagnosis is echocardiography. The aim of our study was to prospectively compare the diagnostic accuracy of echocardiography and cardiac magnetic resonance (MR) imaging in patients with HCM.Twenty-two consecutive patients with a known diagnosis of HCM were prospectively evaluated, with echocardiography and cardiac MR imaging performed within 2 weeks of each other (mean interval 7 days, range 2-14 days). Two experienced radiologists blinded to the previous clinical and imaging findings separately reviewed the images. The following parameters were calculated for both techniques: myocardial mass, wall thickness, end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), systolic anterior motion (SAM) of the mitral valve and degree of myocardial fibrosis (based on the ultrasonic reflectivity at echocardiography and degree of late enhancement at cardiac MR imaging). The statistical correlation was calculated with Student's t test, Spearman coefficient and Fisher's exact test. A value of p0.05 was considered significant.The diagnosis of HCM was confirmed in all patients with both techniques, with absolute agreement in terms of the site of disease. The mean value of myocardial mass presented a statistically significant difference between the two techniques (114 g, p0.001). In contrast, a nonsignificant difference between echocardiography and cardiac MR imaging was found for EDV (102 ml vs 111 ml; p=0.31), ESV (30 ml vs 38 ml; p=0.1), EF (74% vs 68%, p=0.5), SAM (p=0.1) and myocardial fibrosis (p=0.15).Cardiac MR imaging correlates well with echocardiography in defining the morphological and functional parameters useful for the imaging diagnosis of HCM and therefore, in selected cases (poor acoustic window, doubtful echocardiography findings), it may be a valid alternative to echocardiography.