Purpose Despite increasing awareness of accrual challenges, it is unknown if accrual of older patients to breast cancer treatment trials is improving. Methods We examined accrual of older patients to Alliance for Clinical Trials in Oncology systemic therapy breast cancer trials during 1985-2012 and compared disease characteristics and reasons for therapy cessation for older (age ≥ 65 years and ≥ 70 years) versus younger (age < 65 years and < 70 years) participants. To examine accrual trends, we modeled age as a function of time, using logistic regression. Results Overall, 17% of study participants were ≥ 65 years of age. Approximately 15%, 24%, and 24% of participants in adjuvant, neoadjuvant, and metastatic trials were age ≥ 65 years, and 7%, 15%, and 13% were age ≥ 70 years, respectively. The odds of a patient age ≥ 65 years enrolling significantly increased over time for adjuvant trials (odds ratio [OR] per year, 1.04; 95% CI, 1.04 to 1.05) but decreased significantly for neoadjuvant and metastatic trials (OR, 0.62; 95% CI, 0.58 to 0.67 and OR, 0.98, 95% CI, 0.97 to 1.00). Similar trends were seen for those age ≥ 70 years but these were statistically significant for adjuvant and neoadjuvant trials only (OR, 1.05, 95% CI, 1.04 to 1.07; and OR, 0.57, 95% CI, 0.52 to 0.62). In general, those age ≥ 65 years ( v those < 65 years) in adjuvant studies had a higher mean number of lymph nodes involved and more hormone receptor-negative tumors, although tumor sizes were similar. Early protocol treatment cessation was also more frequent in those age ≥ 65 years (50%) versus < 65 years (35.9%) across trials. Conclusion Older patients with breast cancer remain largely underrepresented in cooperative group therapeutic trials. We observed some improvement in accrual to adjuvant trials but worsening of accrual for neoadjuvant/metastatic trials. Novel strategies to increase accrual of older patients are critical to meaningfully change the evidence base for this growing patient population.