Considerable debate exists about the optimal treatment of ductal carcinoma in situ (DCIS). Using electronic data sources, we examined first course treatment patterns among women aged 18 years and older diagnosed with DCIS between 2000-2010 from six Kaiser Permanente (KP) regions. We calculated the proportion of patients receiving breast conserving surgery (BCS), BCS plus radiation therapy, unilateral mastectomy, bilateral mastectomy, and hormone therapy. Multinomial logistic regression was used to assess the association between patient characteristics and treatment. We included 9,437 women: 1,086 (11.5%) African-American; 1,455 (15.4%) Asian; 918 (9.7%) Hispanic; and 5,978 (63.3%) non-Hispanic white. Most cases (42.2%) received BCS plus radiation as their initial treatment. Nearly equal numbers of women received BCS without radiation (28.5%) or unilateral mastectomy (24.6%). Use of bilateral mastectomy was uncommon (4.7%), and most women (72.2%) did not receive hormone therapy has part of their first course treatment. We observed statistically significant differences in treatment patterns for DCIS by KP region and patient age. Predictably, nuclear grade and the presence of comorbidities were associated with first course treatment for DCIS. We observed statistically significant increases in BCS plus radiation therapy and bilateral mastectomy over time. Although still uncommon, the frequency of bilateral mastectomy increased from 2.7% in 2000 to 7.0% in 2010. We also observed differences in treatment by race/ethnicity. Our findings help illustrate the complex nature of DCIS treatment in the United States, and highlight the need for evidence based guidelines for DCIS care.