Nipple discharge is an important clinical entity ranking second only to a lump as the most common complaint among 7,588 patients having breast surgery (560/7,588, or 7.4%). In the office and clinic it is even more common, since many patients can be treated medically and do not require an operation. To be significant, a discharge should be true, spontaneous, persistent, and nonlactational. Nipple discharge can be milky, multicolored and sticky, purulent, clear (watery), yellow (serous), pink (serosanguineous), or bloody (sanguineous). Watery, serous, serosanguineous, and sanguineous discharges are surgically significant; while they are most often caused by intraductal papillomas or fibrocystic disease, they can be due to cancer or a precancerous mastopathy. Among 503 patients operated on for one of these types of discharge, 67 (13.3%) had cancer, and 36 (7.2%) had a precancerous mastopathy. Among the 67 patients with cancer, eight (11.9%) had no palpable mass, 11 (16.4%) had negative cytologic findings, and seven (10.4%) had a negative mammogram. The incidence of associated cancers increases when the discharge is, in order of increasing frequency, serous, serosanguineous, sanguineous, or watery, when it is accompanied by a lump, when it is unilateral and from a single duct, when there are positive cytologic or mammographic findings, and when the patient is more than 50 years of age. Milky discharge caused by galactorrhea is treated medically except when caused by a pituitary adenoma. Multicolored sticky discharge due to duct ectasia is also treated medically except in advanced cases. Purulent discharge caused by an abscess requires drainage and a biopsy of the abscess wall. Except in women less than 30 years of age of in those anxious to have children, we advise a complete central duct excision for patients with surgically significant types of discharge. If done carefully, this procedure can yield good cosmetic results.