On the basis of microlymphaticovenous anastomosis for treating lymphedema of the extremities, the authors developed a microlymphaticovenous procedure to treat congenital lymphedema of the breast and applied it clinically in two patients. The immediate results have been fairly good. The breast and its nipple had been reduced in size and to a nearly normal level. The results are maintained after a half year of follow-up. The fundamentals and techniques of the operation are described and the two case histories are reported. The cases presented here appear to be the first successful clinical attempts to treat lymphedema of the breast by microlymphaticovenous anastomosis. The clinical character of congenital lymphedema, the indication of the microlymphaticovenous anastomosis, and the factors required for success of microlymphatic surgery are discussed.