The HER2 oncogene was recently reported to be amplified and overexpressed in esophageal adenocarcinoma. However, the relationship of HER2 amplification in esophageal adenocarcinoma with prognosis has not been well defined. The scoring systems for clinically evaluating HER2 in esophageal adenocarcinoma are not established. The aims of the study were to establish a HER2 scoring system and comprehensively investigate HER2 amplification and overexpression in esophageal adenocarcinoma and its precursor lesion. Using a tissue microarray, containing 116 cases of esophageal adenocarcinoma, 34 cases of Barrett's esophagus, 18 cases of low-grade dysplasia and 15 cases of high-grade dysplasia, HER2 amplification and overexpression were analyzed by HercepTest and chromogenic in situ hybridization methods. The amplification frequency in an independent series of 116 esophageal adenocarcinoma samples was also analyzed using Affymetrix SNP 6.0 microarrays. In our studies, we have found that HER2 amplification does not associate with poor prognosis in total 232 esophageal adenocarcinoma patients by chromogenic in situ hybridization and high-density microarrays. We further confirm the similar frequency of HER2 amplification by chromogenic in situ hybridization (18%; 21 out of 116) and SNP 6.0 microarrays (16%, 19 out of 116) in esophageal adenocarcinoma. HER2 protein overexpression was observed in 12% (14 out of 116) of esophageal adenocarcinoma and 7% (1 out of 15) of high-grade dysplasia. No HER2 amplification or overexpression was identified in Barrett's esophagus or low-grade dysplasia. All HER2 protein overexpression cases showed HER2 gene amplification. Gene amplification was found to be more frequent by chromogenic in situ hybridization than protein overexpression in esophageal adenocarcinoma (18 vs 12%). A modified two-step model for esophageal adenocarcinoma HER2 testing is recommended for clinical esophageal adenocarcinoma HER2 trial.