A case of histologically confirmed benign lipoma of the right atrium is presented. Magnetic resonance imaging was successfully used to visualize and characterize the tumor previously detected by echocardiography. T1-weighted MR was superior to echocardiography and was in surgical agreement with examination in identifying the relationship of the lipoma to the right atrial wall, the coronary sinus, and the interatrial septum. Comparison of measurements of the tumor's signal intensities on T1- and T2-weighted images and T2 relaxation time with those of surrounding myocardium and mediastinal fat allowed a preoperative diagnosis of lipoma. Magnetic resonance may obviate surgical intervention in selected asymptomatic cases where the diagnosis of benign lipoma appears likely.