Only the kinase domain of ERBB4 has been analyzed in East Asian populations, but a recent large-scale mutation analysis has indicated a higher incidence of mutations in the extracellular domain. Mutations in the extracellular and kinase domains of ERBB4 were examined by direct sequencing in 72 patients with primary lung cancer and 8 cell lines. In addition, ERBB4 expression was determined in 60 patients by quantitative real-time polymerase chain reaction. We investigated the relationship between ERBB4 expression and clinicopathologic characteristics including prognosis. One patient possessed Q793Q polymorphism in the kinase domain. However, we detected no mutations in extracellular or kinase domains of ERBB4. There was no significant difference in the clinicopathologic characteristics including prognosis of patients with high or low expression of ERBB4. The clinical significance of ERBB4 in lung cancers is negligible.