In order to study the causes of postmastectomy lymphedema, venography, lymphangiography and RISA absorption test were performed on the patients following radical mastectomy. Venous obstruction was a rare cause of postmastectomy lymph-edema. Edema patterns in arm lymphangiography were observed in the patients with lymphedema and even in some of the non-edematous upper extremities. The finding of axillary lymphangiography was correlated with the degree of edema of the upper extremity. The absence of adequate lymphatic pathway across the axilla (type 2, collateral and type 3, blocking) was thought to provide the pathologic base for the postmastectomy lymphedema. RISA absorption test also provided precise information of the lymphatic flow in the extremity. It was lower in the patients with edema, as comparied with the patients without edema.