Is it conservative or radical management to excise all fibroadenomas of the breast, especially in women less than 30 years old? Once a definite diagnosis is established by physical examination, fine-needle aspiration cytologic testing, and mammography, is it prudent to monitor women with small fibroadenomas (less than 4 cm in diameter)? We reviewed 498 cases of biopsy-proved fibroadenomas and 17 cases of phyllodes tumors (by biopsy) seen at Los Angeles County/University of Southern California Medical Center from 1986 to 1989. Analysis of patient age and measured tumor size in 203 fibroadenomas and 10 phyllodes tumor specimens revealed similar ranges for both tumors. The mean values were 28.5 years and 2.3 cm for fibroadenomas and 44 years and 3.8 cm for phyllodes tumors. No cases of coincident carcinoma within a fibroadenoma or of metastatic malignant phyllodes tumors were present in this review. As an alternative to excising all breast tumors, cytologically diagnosed fibroadenomas can be monitored, because they have no intrinsic premalignant potential and tend to regress with time. All breast tumors that rapidly increase in size should probably be excised at any age.