Objective : Until now, the effect of isolated, severe tricuspid regurgitation on outcome remains uncertain. So, we sought to evaluate the etiology and clinical outcome of isolated, organic TR. Methods : We analyzed the cause and clinical outcome of 12 patients with isolated, severe tricuspid regurgitation diagnosed by means of 2-dimensional echocardiography between 1997 and 2003 in our institution. We excluded the patients with functional TR by other many causes and with more than 50mmHg of right ventricular systolic pressure. Results : The main cause of TR was incomplete coaptation due to idiopathic annular dilatation (8 of 12) without any other abnormalities in heart. Almost all patients (11 of 12) had severely enlarged RA and RV and the tricuspid annulus was dilated (mean diameter was 43mm). TR velocity was 2.4 짹 0.7 m/s, which is consistent with normal pulmonary pressure. Eight patients were symptomatic at initial presentation (��� NYHA II) and eight patients had chronic atrial fibrillation at diagnosis and remained during follow up period. Five patients (41%) experienced tricupid-related events at 3 years and 7 patients (58%) experienced at 7 years such as heart failure, coumadin toxicity, surgical intervention or death. Only three patients were free of symptom or tricuspid-related events. Even patients asymptomatic at presentation experienced high event rates (3 of 4). Tricuspid operations were performed in 2 patients. The patient perfomed valve replacement was well tolerated without TR. But, in patient with only annuloplasty, TR remained after operation and progressed after two years. Conclusion : Isolated tricuspid regurgitation is rare disease and mostly caused by incomplete coaptation of tricuspid valve with annular dilatation. In contrary to recent datas, our study shows excess morbidity and high event rates in patients irrespective of initial symptom or cause. That is, isolated TR may be serious and progressive disease, so patients shoud be warned about the need for close follow-up and be considered early for surgical intervention. Also, the optimal surgical method in these cases should be more investigated.