Microsurgical lymphaticovenous anastomoses were done on a total of 14 patients. Six upper extremities of six female patients (average age 56.5 years) were operated on with lymphaticovenous anastomoses and were followed up for 17 months or more after surgery (average 25.5 months). Twelve legs of eight patients (average age 44.6 years) also were operated on and followed up for 12 months or more after surgery (average 23.4 months). Among these patients, 33 biopsied lymphatic trunks with lymphedema in 16 extremities of 12 patients were evaluated histologically by light and electron microscopy. Regarding the operative effect in the arms, the decreased circumference of the arms ranged from 2 to 9 cm (average 5.3 cm). The rate of preoperative versus postoperative excess circumference decreased in range from 25 to 94.7 percent (average 65.7 percent). As for the surgical effect in the legs, half the legs showed improvement. These postoperative improvements showed no correlation with the preoperative duration of edema and excess circumference in either the upper or lower extremities. Histologically, in the initial stage of lymphedema, there was destruction of both endothelial cells and smooth muscle cells in the proximal level of the lymphatic trunks. The lumen of some proximal trunks was then occluded by organization with a few small recanalizations, but the distal lymphatics remained patent with minimal destruction of both the endothelial cells and the smooth muscle cells even in the later stage of lymphedema. These results suggest that the occlusions of the lymphatic trunks and degeneration of the smooth muscle cells may start from the proximal ends of the extremities and that the timing of the occlusions and the degeneration of smooth muscle cells may not correspond to the duration of edema. It is also considered that because of the smooth muscle degeneration, the lymph-drainage capacity of the lymphatic trunks may be remarkably weakened in the proximal lymphatics of the extremities. Therefore, it is suggested that the remaining lymphatic drainage function with the smooth muscle cells may correlate with the postoperative improvement of edema. It is also suggested that the preoperative ultrastructural examination of the lymph-drainage capacity may be a suitable method for predicting the surgical effect and operative indication for lymphatic edema in the extremities.