Background Health care reform goals involve more cost-effective methods of delivering health care. The cost-effectiveness of axillary ultrasound-guided core needle biopsy (AUS-CNB) was compared with sentinel lymph node biopsy (SLNB) when evaluating the status of the axilla in operable invasive breast cancer. Study Design We performed an IRB-approved retrospective review of patients undergoing ultrasound of the axilla plus core needle biopsy at our institution from 2007 to 2012. An accuracy of technique and cost analysis (TreeAge Pro 2009) of AUS-CNB vs SLNB was conducted. Results The cohort of 95 patients was divided into 2 groups: clinically positive (CP) (32%) and negative (CN) (68%) axilla. In the CP group, 83% had a suspicious AUS, of which 90% were positive. In the CN group, AUS was suspicious in 70%, with a positive biopsy in 59%. The sensitivity and specificity of AUS-CNB were 90% (95% CI 84.8% to 98.8%) and 100% (95% CI 27% to 59.1%), respectively. Cost estimates comparing AUS-CNB with SLNB demonstrated a cost saving of $236,517 in the CP axilla and $248,490 in the CN axilla, for a total cost savings of $485,007. Conclusions Axillary ultrasound-guided core needle biopsy is a sensitive, diagnostic, surgeon-performed procedure. It is time-saving, cost-efficient, and less invasive, making it a viable option when evaluating the status of the axilla in invasive breast cancer or staging before neoadjuvant chemotherapy.