Melanoma is among the most chemotherapy-resistant malignancies. Numerous new agents have been developed that target specific molecules on cancer cells, including the monoclonal antibody trastuzumab, which targets Her2/neu and has been very beneficial in the treatment of breast cancer. There are conflicting reports in the literature about Her2/neu expression in melanoma specimens, but all of the cohorts studied have been small. We therefore examined Her2/neu expression in a very large cohort of melanoma specimens in order to determine the value of exploring trastuzumab therapy for melanoma patients. Immunohistochemical staining was performed on two tissue microarrays, together containing 600 intact specimens. Expression was evaluated semi-quantitatively and correlated with tumour stage and other clinicopathological data. Of the 600 specimens in the cohort, 31 patients (5.2%) had positive Her2/neu expression. Among the primary cutaneous specimens (n=269), 7% had positive Her2/neu staining, while 3.6% of the recurrent or metastatic specimens (n=331) had positive Her2/neu staining (P=0.06). Among the primary lesions there was no significant correlation between Her2/neu expression, Clark level and ulceration; however, Her2/neu expression was associated with lesions with a Breslow depth of < 2 mm (P=0.05). Using this very large cohort of melanoma specimens, we found only a few cases with aberrant Her2/neu expression, many of them being primary cutaneous lesions rather than recurrent or metastatic lesions. Our findings suggest that drugs that specifically target Her2/neu are not likely to be useful for the treatment of metastatic melanoma or as adjuvant therapy for melanoma patients at high risk for recurrence.