Background: Because of screening mammography, the number of ductal carcinoma in situ (DCIS) survivors has increased dramatically. DCIS survivors may face excess risk of second breast events (SBEs). However, little is known about SBE treatment or its relationship to initial DCIS care. Methods: Among a prospective cohort of women who underwent breast-conserving surgery (BCS) for DCIS from 1997 to 2008 at institutions participating in the NCCN Outcomes Database, we identified SBEs, described patterns of care for SBEs, and examined the association between DCIS treatment choice and SBE care. Using multivariable regression, we identified features associated with use of mastectomy, radiation therapy (RT), or antiestrogen therapy (AET) for SBEs. Results: Of 2,939 women who underwent BCS for DCIS, 83% received RT and 40% received AET. During the median follow-up of 4.2 years, 200 women (6.8%) developed an SBE (55% ipsilateral, 45% invasive). SBEs occurred in 6% of women who underwent RT for their initial DCIS versus 11% who did not. Local treatment for these events included BCS (10%), BCS/RT (30%), mastectomy (53%), or none (6%); only 28% of patients received AET. Independent predictors of RT or mastectomy for SBEs included younger age, shorter time to SBE diagnosis, and RT or AET for the initial DCIS. Conclusions: A sizable proportion of patients with SBEs were treated with mastectomy, most especially those who previously received RT for their initial DCIS and those who developed an ipsilateral SBE. Despite the occurrence of an SBE, relatively few patients received AET. Future studies should investigate optimal treatment approaches for SBEs, including the benefit of mastectomy versus lumpectomy for an ipsilateral SBE and the benefit of AET for a hormone-receptor–positive SBE contingent on AET use for the initial DCIS diagnosis.