Breast ultrasound has mainly been used for differentiation of cystic and solid lesions. With high resolution technique, which was introduced several years ago, early cancers can now be detected by ultrasound. In this study, 1016 women were examined within 3 months. Mammography was used independently. According to the expected prevalence, 4 nonpalpable carcinomas were detected by sonography. The study proves that high-quality ultrasound equipment allows a primary detection of subclinical breast cancers. In premenopausal patients the sensitivity of mammography is reduced. Therefore, ultrasound should be used complementary to mammography in this age group. Widespread use is not possible due to a deficiency in experienced staff. However, in experienced centres, ultrasound could be used as a supplement to mammographic screening to prove if breast cancer mortality in premenopausal women can be reduced.