Our study describes the patterns of adjuvant chemotherapy use in women 20 years of age or older with stage I, stage II, or stage IIIA breast cancer in New Mexico from 1991 through 1997. The rates of chemotherapy use for stage I, stage II, and stage IIIA were 11%, 47%, and 68%, respectively. Across all tumor stages, the use of chemotherapy decreased substantially with increasing age (P < 0.001 for trend). Overall, 66% of women younger than 45 years of age received chemotherapy compared with 44% of women 50 to 54 years of age, 31% of women 55 to 59 years of age, and 18% of women 60 to 64 years of age. In women age 65 to 69 years and those older than 75 years, only 12% and 3%, respectively, received chemotherapy. The decreasing pattern of chemotherapy use with age was maintained after adjustment for such prognostic factors as node status, hormone receptor status, and other treatments received.