Clinical studies evaluating the role of magnetic resonance imaging (MRI) in patients with hypertrophic cardiomyopathy are scanty. To assess the capability of MRI to define the presence, distribution and severity of left ventricular hypertrophy, the prevalence and clinical implications of right ventricular hypertrophy, the prevalence and clinical implications of myocardial structural abnormalities, MRI and echocardiography were performed in 37 unselected patients (age 10-72 years, mean 38 +/- 19) with hypertrophic cardiomyopathy. The concordance between the two methods was 100% in the diagnosis and classification of left ventricular hypertrophy as asymmetric, concentric or apical. A significant linear correlation was found between echocardiography and MRI measurements of interventricular septum (r = 0.69, p < 0.0001, SEE = 4) and left ventricular posterior wall (r = 0.67, p < 0.0001, SEE = 2.4). Right ventricular hypertrophy (right anterior wall diastolic thickness > 5 mm) was disclosed by MRI in 23/33 patients (70%). In this group, left posterior wall thickness and left atrial diameter were higher (15 +/- 4 versus 11 +/- 2 mm, p < 0.01 and 45 +/- 9 versus 38 +/- 5 mm, p < 0.05 respectively). On T2 weighted sequences, areas of reduction of signal intensity, probably caused by myocardial fibrosis, were detected in 16 cases (43%). This group was characterized by a higher value in maximal septal thickness (26 +/- 7 versus 21 +/- 6 mm, p < 0.05) and in maximal left posterior wall thickness (15 +/- 9 versus 7 +/- 8 mm, p < 0.01). All the 3 cases with dilated and hypokinetic left ventricle showed this type of tissue abnormality.(ABSTRACT TRUNCATED AT 250 WORDS)