PURPOSE: To evaluate the ultrasonomammographic findings of breast fibroadenoma. METHODS AND MATERIALS:We evaluated the ultrasonographic findings of histopathologically proved 135 fibroadenomas in 103 patients from January 1986 to September 1990, retrospectively. The ultrasonographic examinations were performed with a hand held linear array 5MHz transducer(Acuson 128(USA). Aloka 650, 280(Japan)). A sonopad was also used during the examinations. RESULTS: The common ultrasonographic findings of fibroadenomas usually showed smooth contour in 120 lesions(88.9% ), oval or round shape in 114 lesions(84.4%), uniform homogeneous echogenecity in 106 lesions(78.5% ), intermediate hypoechoic internal echo pattern in 105 lesions(77.8%), thin boundary echo in 117 lesions(86.7%), lateral shadowings in 97 lesions(72%), and posterior acoustic enhancement in 56 lesions(41%). The longitudinal/transverse ratio of fibroadenoma was revealed between 0.2 and 1.14 (mean 0.58) and usually under 1.0 (68.9%). CONCLUSION: Finally, most of fibroadenomas are easily diagnosed by ultrasonography but if differential diagnosis from malignant breast mass is difficult due to atypical appearance, other combined modalities such as filmmammography, fine needle aspiration biopsy and MRI are necessary.