The structure and the function of the peripheral lymph channels have been investigated, but the thoracic duct has not. This study used magnetic resonance thoracic ductography for 2 patients with idiopathic lymphedema to evaluate the configuration of the thoracic duct in these patients. Anomalies of the thoracic duct were detected in both cases. This result suggests that deformity of the thoracic duct is one of the causes of idiopathic lymphedema. Characterization of the etiology could lead to a breakthrough in resolving the occurrence of idiopathic lymphedema and developing a treatment procedure for it. In addition, visualization of the thoracic duct may assist in selecting the optimal therapy for each idiopathic lymphedema patient.