The demonstration of the effectiveness of chemotherapy in both premenopausal and postmenopausal women, regardless of estrogen receptor (ER) status, raises the question of whether all breast cancer patients should receive chemotherapy. Several patient groups with such a favorable long-term prognosis that they will obtain an extremely small benefit from chemotherapy can be identified. They include patients with lymph node-negative tumors of 1 cm or less in size, those with grade 1 tumors between 1.1 and 2.0 cm in size, and those with tumors of favorable histologic type (tubular and mucinous) up to 3 cm in size. A patient subgroup in which it is not clear that the benefits of chemotherapy routinely exceed the risks is postmenopausal women with ER-positive, lymph node-negative cancers receiving tamoxifen. There is a wide variation in prognosis in this group, and chemotherapy should be reserved for those at high risk of recurrence. Finally, no benefit for chemotherapy in women aged 70 years and older has been identified. The high rate of death from causes other than breast cancer may negate small survival benefits, and after adjustment for quality of life, the duration of treatment exceeds the gain in life expectancy.