To evaluate differences in use of sentinel lymph node biopsy (SLNB) by age and race in Medicare recipients with early-stage breast cancer, we examined Surveillance, Epidemiology and End Results—Medicare linked data for women undergoing breast conserving surgery for stage I or II breast cancer, including axillary staging, between January 2000 and December 2002. Multivariable generalized linear modeling with generalized estimating equations was used to identify predictors of receiving SLNB versus standard axillary lymph node dissection as the primary axillary staging modality. Women were significantly less likely to receive SLNB as their primary staging procedure if they were African American (OR 0.65), greater than 80 years of age (OR 0.71 vs. age <70), or dually eligible for Medicare and Medicaid (OR 0.61). Tumor characteristics, including well-differentiated histology and stage I disease, were associated with increased likelihood of SLNB, but estrogen receptor status was not a significant predictor. Women treated at an institution affiliated with an NCI cooperative research group had significantly greater likelihood of receiving SLNB (OR 2.31). Likelihood of receiving SLNB increased for women diagnosed in 2001 and 2002 compared with 2000. Significant disparities exist in receipt of SLNB in the Medicare population, with African Americans, the elderly, and economically disadvantaged patients being less likely to receive this innovative and morbidity-sparing procedure. These findings continue a previously observed pattern of reduced access to state of the art breast cancer care among underserved populations.