To assess the relationship between the distribution of hypertrophy and electrocardiographic changes in patients with hypertrophic cardiomyopathy, magnetic resonance imaging and ECG findings were correlated in 25 patients with apical hypertrophy (group I), 15 patients with both apical and basal hypertrophy (group II), and 11 patients with hypertrophy localized to the basal left ventricle (group III). The number of precordial leads with negative T waves (-0.5 mV or more) was greater in group I than in groups II and III (I = 3.0 +/- 1.5, II = 1.7 +/- 1.5, III = 0.3 +/- 0.6; p < 0.01). Giant negative T waves (-1.0 mV or more) in precordial leads were found in 13 patients (52%) in group I and five patients (33%) in group II but were not found in group III. In contrast, tall positive T waves (> or = 1.0 mV) in precordial leads were found in two patients (13%) in group II and five (45%) in group III but were not found in group I. These results suggest that the distribution of hypertrophy in patients with hypertrophic cardiomyopathy produces a particular T wave polarity in precordial leads.