Women with ductal carcinoma in situ (DCIS) of the breast represent a growing cancer survivor population with a diagnosis of uncertain malignant potential. These survivors face an absence of scientific guidelines regarding lifestyle changes that can help to prevent a breast cancer recurrence. In this first report from the Wisconsin In Situ Cohort (WISC) study, we examine how women are currently changing their lifestyle behaviors and medication use following a diagnosis of DCIS. At study entry (1997-2006), 1,959 subjects (78% of eligible) with DCIS were identified from the Wisconsin cancer registry and administered an interview assessing behaviors prior to diagnosis. Follow-up interviews were completed every 2 years after the initial interview, beginning in 2003 and continuing through 2006. After adjusting for age and calendar year, women were 2.2 kg (95% CI 1.4, 3.0) heavier, 35% (95% CI 20, 47) less likely to be a smoker, 19% (95% CI -1, 43) more likely to use non-steroidal anti-inflammatory drugs, and 57% (95% CI 26, 95) more likely to use antidepressants after a DCIS diagnosis compared to 1 year prior to diagnosis. Use of postmenopausal hormones decreased sharply (OR = 0.06; 95% CI 0.04, 0.09) following a DCIS diagnosis. These findings indicate that women make substantial changes in their behaviors after a DCIS diagnosis. This cohort will be further monitored to evaluate the association between these behaviors and health outcomes following DCIS.