PURPOSE: To determine the relationship between fibrocystic change and parenchymal pattern and fibroadenoma on mammogram. MATERIALS AND METHODS: Mammograms of 135 patients with histologically-diagnosed fibrocystic disease after excisional biopsy were retrospectively analyzed and correlated with pathologic specimens. Classification ofthe parenchymal pattern was based on Wolfe's method. RESULTS: On mammogram, we observed abnormality in 88 out ofthe 135 cases ; these latter consisted of 70 cases of DY, 30 of P2, 20 of P1, and 15 of Nl, following Wolfe's parenchymal patterns. Among the 88 abnormal cases we observed 37 cases of mass with clear boundaries, five cases of mass with unclear boundaries, 22 with clustered microcalcifications, six with macrocalcifications and 18 with asymmetric dense breast. Histologic examination revealed a varying composition of stromal fibrosis, epithelialhyperplasia, cyst formation, apocrine metaplasia, etc. Histologically fibroadenomatoid change in 18 cases was appeared as a radiopaque mass on mammogram, especially in those cases where the change was well-defined, which were all except three. CONCLUSION: Fibrocystic disease was prevalent in Wolfe's P2 and DY patterns(about 80 %).About 40 % of fibrocystic change appearing as a well defined mass on mammogram showed fibroadenomatoid change histologically and was difficult to differentiate from fibroadenoma. Fibrocystic disease should therefore be included in the differential diagnosis of a mass which on mammogram is well-defined.