Mondor's disease is a rare entity characterized by sclerosing thrombophlebitis classically involving one or more of the subcutaneous veins of the breast and anterior chest wall. It is usually a self-limited, benign condition, despite of rare cases of association to cancer. We present the case of a 32 year-old female, breast-feeding, who went to emergency due to left mastalgia for the past week. She was taking antibiotics and non-steroidal anti-inflammatory drugs, previously prescribed for suspicious of mastitis, for three days, with no clinical improvement. Physical examination showed an enlarged left breast, an axillary lump and a painful cord-like structure in the upper outer quadrant of the same breast. Ultrasound scan showed a markedly dilated superficial vein in the upper outer quadrant of left breast. The patient was given a ventropic therapy and was kept in anti-inflammatory, with progressive pain improvement. Ultrasound control was performed after four weeks, showing reperfusion.