Mondor's disease or thrombophlebitis of the subcutaneous veins of the chest region is an uncommon condition and is rarely associated with breast cancer. From January 1980 to June 1990, 63 cases of Mondor's disease were diagnosed (57 women and 6 men). In 31 patients, no apparent cause was determined (primary disease), whereas in 32 cases, the disease was secondary because the etiopathogenesis could be discerned. The identified potential causes were three cases of myentasis (all in men), eight cases of accidental local trauma (seven in women), seven cases of iatrogenic origin (three surgical breast biopsies, one skin biopsy, one needle biopsy, one mastectomy, and one reconstruction operation), six cases of inflammatory process, and eight cases associated with breast cancer (all females). Three of the tumors were less than 1 cm in diameter. The authors performed conservative surgery in four patients and demolitive in the other four. In this series, the incidence of breast cancer in association with Mondor's disease was the highest yet reported (12.7%). It was concluded that Mondor's disease may at times be caused by breast carcinoma. This association is by no means exceptional and implies that mammography should always be performed for Mondor's disease, even when the results of a physical examination are negative.