Breast ultrasound (US) was performed, with either an automated or a hand-held unit or both, on 1,212 patients. Of 612 asymptomatic patients, 118 (19.3%) had solitary cysts; ten (1.6%), multiple cysts; and 29 (4.7%), benign masses; however, US depicted only one (0.2%) nonpalpable mammographically undetected carcinoma. In 513 patients with palpable masses (n = 396) and with mammographically detected masses (n = 117), US was useful in avoiding an unnecessary biopsy in 113 (22.0%), leading to aspiration of a cyst in 26 (5.1%), monitoring multiple cysts in 31 (6.0%), avoiding aspiration of a solid mass in 65 (12.7%), supporting biopsy of an equivocal solid mass in 91 (17.7%), and demonstrating a nonpalpable mammographically detected carcinoma in six (1.2%). In 224 patients with either palpable or mammographically visible masses who underwent both methods of US, the 4.5-MHz or 3.9-MHz automated unit depicted the abnormality in 119 (53.1%) and the 7.5-MHz hand-held unit, in 171 (76.3%). Of 18 cancers evaluated with both methods, all were detected with the hand-held unit and only 12 were seen with the automated unit.