In a prospective study of 235 tissue masses verified histologically, we examined the diagnostic contribution of ultrasound in comparison to mammography. When the two methods were combined, 96.8% of all malignant neoplasms could be diagnosed correctly. Most (90.5%) were found by mammography alone and 4.8% were detectable by ultrasonography but not by mammography. Despite relatively good results in the evaluation of solid masses, it is not advisable to omit tissue examination. The superiority of ultrasound over mammography in the diagnosis of cystic lesions could lead to a significant reduction in needle aspirations and biopsies.