Purpose : To analyze the dynamic MR imaging of breast fibroadenoma according to the histologic type fordifferentiation from breast carcinoma. Materials and Methods : Dynamic MR images of 26 lesions from 22 breasts in19 patients showing atypical clinical features or film mammogram and ultrasound manifestations were performed. Weanalyzed the speed and the maximal amount of contrast enhancement and the patterns, such as shape, border, andinternal signal intensity, among the histologic types during five minutes after contrast injection. Results : Thespeed and maximal amount of contrast enhancement of fibroadenoma were in descending order of myxoid, sclerotic,glandular, and calcified type. Among those, the value of maximal amount of contrast enhancement of myxoid andsclerotic type were more than 700 NU, but only myxoid type was enhanced more than 700 NU within the first 1 minuteafter contrast injection, similar to the findings to carcinoma. In general, fibroadenoma showed the tendency ofsmooth surface(69%), well-defined border(88%) with safety rim, and internal homogeneous signal intensity(65%).However, sclerotic type of fibroadenoma had relatively high incidence of heterogeneous internal signalintensity(78%) after Gd-DTPA injection. Conclusion : Dynamic MR imagins of atypical breast fibroadenoma mimickingbreast malignancy was very useful to differentiate it from carcinoma and had the benefit of classifyingfibroadenoma according to its histologic types.