The degree of adherence with evidence-based guidelines for the use of breast ultrasonography was determined in clinical practice of radiologists in six hospitals. Additional ultrasonography was performed in 2,272 (53%) of all 4,257 patients referred for mammography. High adherence rates (mean: 95%) were observed for guidelines recommending ultrasonography in patients referred for palpable breast masses and abnormal screening and diagnostic mammograms. Lower adherence rates (mean: 81%, Pearson correlation coefficient= -0.57; p=0.001) were found for guidelines advising against additional ultrasonography in patients referred for breast symptoms, a known benign abnormality, a family history or anxiety of breast cancer. The overuse of ultrasonography in 442 patients and underuse in 95 patients led to five additional false-positive results. It was concluded that the guidelines seem workable and feasible in clinical practice and that the current daily routine of diagnostic breast imaging corresponded to a great extent to the guidelines proposed.