Background: Despite sporadic case reports of development of significant tricuspid regurgitation (TR) late after successful left-sided valve surgery, the incidence and factors associated with TR development have not been seriously investigated. Methods: Preoperative echocardiography of patients who underwent mitral and/or aortic valve surgery from 1995 to 2000 was reviewed. Patients with significant TR (grade ���3/4) or organic tricuspid valve (TV) abnormality were excluded. Using follow-up echocardiography (74.1짹26.9 months after surgery), the severity of TR was graded (+1~+4) based on spatial distribution of distal TR jet in color Doppler. Development of late significant TR was defined as increase of TR by ���2 grade compared with preoperative findings. Results: A total of 654 patients was enrolled and among them 51 (7.9%) showed development of late significant TR. Patients who underwent both mitral and aortic valve surgery showed significantly higher incidence (Figure, left). Old age, atrial fibrillation, rheumatic etiology and female gender were independent factors associated with late significant TR. The 5 year event-free survival rate was significantly lower in patients with late TR (90.7짹2.5% vs 84.0짹10.4%, p=0.02). Conclusions: Rheumatic valvular heart disease without definite evidence of direct TV involvement is a risk factor of late TR development, and special consideration on timing of surgery for these patients with high risk factors seeems to be necessary.