The use of tissue microarray (TMA) technology may substantially reduce the costs of routine testing of breast carcinomas for human epidermal growth factor receptor 2 (HER2) status. After a preliminary pilot study comparing the TMA results with those obtained on whole section, which showed an excellent agreement (with kappa values >0.90) for both immunohistochemical and fluorescent in situ hybridization (FISH) method, we introduced the TMA technique in our routine work. A total of 1158 invasive breast carcinomas were submitted for the determination of HER2 status, which was assessed in 74 weekly runs. One hundred twenty-five of 1084 surgical specimens (11.5%) were judged as unsuitable for inclusion into TMAs. In 32 of 959 tumors included in TMAs (3.3%), the respective cores were uninformative, and HER2 status was determined on whole sections. Thus, HER2 status was finally determined on TMA in 927 cases (81.1%). A typical weekly run comprised 1 TMA (consisting, on average, of 13 tumors), 2 whole sections of surgical specimens and 1 whole section of core needle biopsy, and the number of processed slides for each method decreased from 16 to 4 per week. In all, 14.7% of tumors were HER2 positive by FISH. In both TMAs and whole sections, immunohistochemical results were in good agreement with FISH for cases scored as 0/1+ (98% and 97%) and for those scored as 3+ (96% and 87%), whereas concordance was poor in cases scored as 2+ (30% and 13%, respectively).