The goal of this study was to assess the performance characteristics of the Automated Cellular Imaging System (ACIS III) for HER2 immunohistochemical analysis. The study was performed on 187 biopsy slides from patients who underwent HER2 testing between January and February 2008. Three scoring methods by the ACIS III were compared with the manual score and fluorescence in situ hybridization (FISH) results for HER2 amplification. The equal distribution score (EQD) method, in which 2 areas each of high-, moderate-, and low-intensity staining were measured, most closely matched the FISH HER2 amplification result. The numbers of immunohistochemically negative (0 or 1+)/FISH+ cases were equivalent for all methods. The EQD method had significantly fewer 2+ cases (n = 16) (P < .001) vs the manual method (n = 35) and yielded a higher positive predictive value (38%) for HER2 amplification compared with the manual method (20%). The EQD method may more accurately identify FISH-amplified HER2 cases with fewer 2+ cases that would be "reflexed" to FISH compared with the manual method.