Cardiac rhabdomyoma occurs frequently in patients with tuberous sclerosis (TS). Although there have been case reports of detection of cardiac rhabdomyoma by 2-dimensional echocardiography, no study has examined the frequency of cardiac rhabdomyoma detected by cardiac ultrasound in patients with TS. Echocardiography was performed in 16 consecutive patients with TS. Physical examination revealed normal cardiac findings in each. Discrete areas of increased acoustic density were found in 8 of the 16 patients (50%). The maximum diameters ranged from 3 to 20 mm. Multiple areas were found in 3 of 8. The left ventricle was involved in 5 of the 8. Six masses were intracavitary and 8 were intramyocardial. No atrial masses were seen. Left ventricular size and function were normal. Although other tumors cannot be excluded, the diagnosis of cardiac rhabdomyoma is almost certain in these young patients with TS. The male predominance and the high incidence of intracavitary and left ventricular masses are similar to those in reported autopsy series, also supporting the diagnosis of cardiac rhabdomyoma. The prognosis and potential for growth of these masses are not known, but can be determined by longitudinal follow-up. Cardiac ultrasound should be considered for all patients with TS regardless of physical findings.