In a series of 8,703 breast operations, nipple discharge was the presenting symptom in 7.4% of cases. It is even more common in the office and clinic since many discharges can be treated medically. To be significant, a discharge should be true, spontaneous, persistent, and nonlactational. Of the 7 basic types, i.e., milky, multicolored and sticky, purulent, clear (watery), yellow (serous), pink (serosanguineous), and bloody (sanguineous), the last 4 are the surgically significant ones. Of the 586 patients operated on for one of these types of discharge, the majority had a benign etiology, i.e., intraductal papillomata (48.1%) and fibrocystic changes (32.9%), but 14.3% were due to cancer and another 7.3% to precancerous mastopathy. In the 84 patients with cancers, the false-negative rate for mammography was 9.5% and was 17.8% for cytology. There was no palpable mass in 13.1% of patients. There was an increasing likelihood of the discharge being due to cancer when the discharge was, in order of increasing frequency, yellow, pink, bloody, or watery, when it was accompanied by a lump, when it was unilateral and from a single duct, when the mammogram or galactogram and the cytology were positive, and when the patient was over 50 years of age. Milky discharges are usually treated medically unless they are due to a pituitary adenoma. If the cause cannot be found and eradicated, bromocriptine is the drug of choice. Multicolored sticky discharges are also treated medically, chiefly by nipple hygiene, except when advanced. Purulent discharges are treated with appropriate antibiotics but abscesses need drainage and a biopsy of the wall. Except in women under 35 years of age or in those anxious to have children, surgically significant discharges are treated by central duct excision. Good cosmetic results can be obtained with careful technique and the danger of a recurrent discharge is eliminated.