PURPOSE: To examine the associations between sentinel lymph node biopsy (SLNB) and complications among older patients who underwent breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS). METHODS: We identified women from the Surveillance, Epidemiology, and End Results-Medicare dataset aged 67-94 years diagnosed during 1998-2011 with DCIS who underwent BCS as initial treatment. We assessed incidence of complications, including lymphedema, wound infection, seroma, or pain, within 9 months of diagnosis. We used Mahalanobis matching and generalized linear models to estimate the associations between SLNB and complications. RESULTS: Our sample consisted of 15,515 beneficiaries, 2409 (15.5%) of whom received SLNB. Overall, 16.8% of women who received SLNB had complications, compared with 11.3% of women who did not receive SLNB (p < 0.001). Use of SLNB was associated with subsequent mastectomy but not radiotherapy. Multivariate analyses of the matched sample showed that, compared with no SLNB, SLNB use was significantly associated with incidence of any complication [adjusted odds ratio (AOR) 1.39; 99% confidence interval (CI) 1.18-1.63], lymphedema (AOR 4.45; 99% CI 2.27-8.75), wound infection (AOR 1.24; 99% CI 1.00-1.54), seroma (AOR 1.40; 99% CI 1.03-1.91), and pain (AOR 1.31; 99% CI 1.04-1.65). Sensitivity analyses excluding patients who underwent mastectomy yielded qualitatively similar results regarding the associations between SLNB and complications. CONCLUSIONS: Among older women with DCIS who received BCS, SLNB use was associated with higher risks of short-term complications. These findings support consensus guidelines recommending against SLNB for this population and provide empirical information for patients.