In this review we summarize the data on epidemiology and natural history of functional tricuspid valve regurgitation as it applies to surgery for mitral valve disease. Tricuspid regurgitation in the context of mitral valve disease is frequent and is associated with substantial reduction in survival and quality of life. In many patients, the correction of left-sided cardiac lesions does not lead to resolution of tricuspid regurgitation. Significant tricuspid regurgitation after mitral valve surgery portends a poor prognosis, a course that is often not altered by subsequent surgical therapy. Although a liberal approach to tricuspid annuloplasty is widely practiced, the evidence that this approach alters the natural history of functional tricuspid regurgitation is not yet available, so it is not certain how much of the negative impact of tricuspid regurgitation is causative, rather than confounding, and to what degree we will improve long-term outcomes of mitral valve surgery by liberal tricuspid annuloplasty.