Background: Antiestrogen (anti-e) use in estrogen receptor–positive (ER+) ductal carcinoma in situ (DCIS) has been shown to reduce the incidence of noninvasive and invasive breast cancer. Few studies have evaluated factors associated with anti-e recommendation in ER+ DCIS. Methods: The California Cancer Registry was queried for female patients diagnosed with ER+ DCIS and treated with lumpectomy or unilateral mastectomy from 2004 to 2011. Patient demographics, comorbidities, and clinical characteristics were analyzed for association with anti-e recommendation. Results: Of 5,527 patients identified, 76.4% patients underwent lumpectomy and 23.6% underwent unilateral mastectomy. Of the total cohort, 31.6% patients were recommended anti-e therapy, 60.4% were not, and the remaining 8.0% were recommended anti-e, but administration was not documented. Performance of lumpectomy predicted anti-e use compared with mastectomy (odds ratio [OR], 2.08; 95% CI, 1.77–2.43). Asian/Pacific Islanders were more often recommended anti-e therapy when compared with whites (OR, 1.28; 95% CI, 1.10–1.49). Patients younger than 70 years were more often recommended anti-e (age, 18–49 years: OR, 1.38; CI, 1.12–1.71; and age, 50–69 years: OR, 1.43; CI, 1.20–1.71). Conclusions: Despite current guidelines to consider the use of anti-e therapy, recommendation of anti-e after surgical treatment of DCIS is low, having been recommended to 40% of patients, and used by fewer than one-third. Significant predictors include lumpectomy compared with unilateral mastectomy, Asian/Pacific Islander race, younger age, and number of comorbidities. Further work is merited to understand patterns of anti-e therapy recommendation by providers in patients with DCIS.