Transforming growth factor-$eta$ is a pleiotropic growth factor that has enthralled many investigators for approximately two decades. In addition to many reports that have clarified the basic mechanism of transforming growth factor-$eta$ signal transduction, numerous laboratories have published on the clinical implication/application of transforming growth factor-$eta$. To name a few, dysregulation of transforming growth factor-$eta$ signaling plays a role in carcinogenesis, autoimmunity, angiogenesis, and wound healing. In this report, we will review these clinical implications of transforming growth factor-$eta$.