The value of cross-sectional echocardiography in the early diagnosis of right ventricular (RV) dysplasia in asymptomatic patients has been assessed. Criteria that defined RV dysfunction and structural abnormalities were developed from 38 normal subjects. Of 136 patients admitted into the study program, 40 (29.4%) had an echocardiogram suggestive of RV dysplasia using the following criteria: mild dilatation of the right ventricle (normal range defined as the 95% confidence limit of the values in the control group); localized bulge and dyskinesia of the infero-basal wall; structural changes of the moderator band; isolated enlargement of RV outflow tract; apical dyskinesia and trabecular disarrangement. Holter monitoring and a maximal exercise stress test at entry into the study and during the follow-up (mean 42, range 18-82 months) demonstrated serious ventricular arrhythmias, and RV endomyocardial biopsy confirmed the diagnosis of RV dysplasia in most of these patients, characterized by an electrical instability of RV myocardium (82.5%). During the follow-up, a marked enlargement of RV cavity appeared in three other patients, and RV endomyocardial biopsy demonstrated the typical findings in all patients.