Mondor's disease, superficial thrombophebitis of the breast, is an uncommon self-limiting condition. Surgical procedures and trauma were the common known causes. The objective of this study was to evaluate the incidence of Mondor's disease in different breast operations in lower risk of breast cancer area over a 6-year period and to identify its causes, clinical features, related surgical factors and associated breast cancer. Eighty-four cases of Mondor's disease were obtained from 9657 new patients in the breast clinic of Kaohsiung Medical University Hospital between January 1991 and December 1996. The incidence per year was close (0.84%-0.96%) although the number has been increasing each year. In 23 cases, no definite cause was diagnosed, whereas in 61 cases, the disorder was secondary because the pathogenesis could be discerned. The identified causes included forty-three cases caused by breast surgery, two cases associated with breast cancer and sixteen cases with other benign causes. Although the incidence did not differ significantly between breast surgery (0.95%) and non-surgical causes (0.79%), the highest incidence, 1.52%, occurred when excision through circumareolar incision and tunnel procedure for cosmesis (25 cases in 1634 excisions) were used, and the lowest 0.69% when excisions through direct incision (14 cases in 2004 excisions) were performed. (P < 0.05) The other incidence rates were 1.56% in breast conserving surgery which is higher than 0.37% following mastectomy. The incidence of the disease was higher (4.28%) when the distance of the breast lesion was more than 3 cm from the areolar edge, compared to 1.20% for the 2 cm group and 0.32% for the 1 cm group (P < 0.05) in tunnel procedures. The incidence of Mondor's disease during breast surgery was not significantly different in different breast quardrants. Although Mondor's disease is a benign, self-limiting condition, a high incidence developed in the excision biopsy through circumareolar incision with tunnel procedure when the distance from the breast lesion to the areolar edge was more than 3 cm. To prevent this complication, the tunnel procedure in breast biopsy should be avoided. The incidence of Mondor's disease associated with breast cancer was low (2.4%) in the lower-incidence breast cancer area from this series, but awareness of the condition is recommended.