Purpose The mechanisms by which trastuzumab imparts clinical benefit remain incompletely understood. Antibody-dependent cellular cytotoxicity via interactions with Fcγ receptors (FcγR) on leukocytes may contribute to its anti-tumor effects. Single nucleotide polymorphisms (SNPs) in FCGR3A and FCGR2A genes lead to amino acid substitutions at positions 158 and 131 respectively and affect binding of antibodies to FcγR such that 158V/V and 131H/H bind with highest affinity. This study aimed to determine whether high affinity SNPs are associated with disease free survival (DFS) among patients with HER2-positive non-metastatic breast cancer. Experimental Design Genomic DNA was isolated from 1,286 patients enrolled in a trial of adjuvant trastuzumab-based chemotherapy. Genotyping was performed using Sanger sequencing and Sequenom mass spectrometry. Results 1,189 patient samples were successfully genotyped for FCGR3A and 1,218 for FCGR2A. Compared to the overall results of the BCIRG006 study, in the subset of patients genotyped in this analysis, a less robust improvement in DFS was observed for the trastuzumab arms compared to control arm (HR=0.842, P=0.1925). When stratified for prognostic features, the HR in favor of trastuzumab was consistent with that of the overall study (HR=0.74, P=0.036). No correlation between DFS and FCGR3A/2A genotypes was seen for trastuzumab-treated patients (158V/V vs V/F vs F/F, P=0.98; 131H/H vs H/R vs R/R, P=0.76; 158V/V and/or 131H/H vs others, P=0.67). Conclusion This analysis evaluating the association between FCGR3A/2A genotypes and trastuzumab efficacy in HER2-positive breast cancer did not demonstrate a correlation between FCGR3A-V/F and FCGR2A-H/R SNPs and DFS in patients treated with trastuzumab.