Background Margin assessment is an essential component of breast conservation surgery (BCS). Re-excision of infiltrated margin(s) detected on paraffin section histology (PSH) needs reoperation, adding time, inconvenience and cost. Intra-operative assessment of margins using frozen section histology (IFSH) can potentially obviate need for reoperation, thus facilitating one-step oncologically complete BCS. Methods IFSH and PSH reports of consecutive patients undergoing BCS (2010-2020) were reviewed. Accuracy and cost-efficacy of IFSH were assessed, considering PSH as gold standard. Cost of achieving oncologically complete BCS in whole cohort with IFSH (Scenario-A) was calculated and compared using appropriate statistical tests, with hospital costs for the cohort in a hypothetical Scenario-B, where IFSH was presumed not to have been used and all patients with infiltrated margin(s) on PSH would have been re-operated. Results Of the 367 patients screened, 39 were excluded due to incomplete IFSH data. Of 328 patients analyzed, 59 (18%) had one or more margins were reported infiltrated on IFSH, managed by re-excision or mastectomy in the same sitting, thus avoiding a reoperation. Additional 8 (2.4%) had involved margins on PSH (False negative IFSH). Significantly higher number of reoperations (p \ 0.001) would have been needed in scenario-B. Average cost of the first operation with use of IFSH was Indian Rupees (INR) 25791 which included INR660 as IFSH cost. The average cost of reoperation was INR23724 which could be avoided in 59 (18%) by use of IFSH. The average cost per patient to achieve oncologically complete surgery in scenario A utilizing IFSH was significantly lower (p = 0.001) by INR3101 (11.7%), c.w. that in scenario B. Significant cost-saving with IFSH was maintained in cost-efficacy analysis undertaken with various higher and lower costs assumptions. Conclusions Use of IFSH facilitates one-step oncologically complete BCS in majority of patients and results in considerable cost saving, resulting in avoidance of reoperations, besides preventing patient anxiety and delay in adjuvant treatment. Trial Registration Clinical Trials Registry-India (CTRI/2021/08/035896).