B7-H3 is a member of the B7 family thought to be a co-regulatory factor of antigen-specific T-cell immune response via co-stimulatory and co-inhibitory receptors. We evaluated its potential expression in head and squamous cell carcinoma (SCC) cell lines, and in clinical tissue samples obtained from 37 patients with human hypopharyngeal SCC. All head and neck SCC cell lines tested expressed both the B7-H3 gene and cell surface protein. The staining intensity of immunoreactivity by tumor cells was blindly evaluated by two head and neck surgeons and the results were categorized into 4 grades according to staining intensity. Eighty-seven percent of patients expressed B7-H3. B7-H3 expression was inversely correlated with the number of tumor infiltrating CD8+ T-cells (r=-0.4339, p=0.023). Patients who developed distant metastasis after tumor-free periods showed significantly higher B7-H3 expression scores compared to patients who did not develop distant metastasis during follow-up periods (p=0.048). Distant metastasis control ratio in patients with strong B7-H3 expression was significantly lower compared to that in patients with no to intermediate B7-H3 expression (p=0.040). Cause-specific survival ratio in patients with strong B7-H3 expression was significantly lower compared to that in patients with no to intermediate B7-H3 expression (p=0.028). Moreover, multivariate analysis revealed that strong B7-H3 expression was an independent prognostic factor in tumor-specific death in hypopharyngeal SCC (hazard ratio: 9.803, confidence interval: 0.018-0.539, p=0.0110).