The development of laryngeal squamous cell carcinomas (LSCC) is strongly influenced by the host immune system. Indoleamine 2,3-dioxygenase (IDO) can promote and maintain an immunosuppressive microenvironment which can impede the efficacy of anticancer responses. The purpose of the current study is to investigate the prognostic value of intratumoral IDO expression in LSCC. The expression of IDO protein was retrospectively assessed by immunohistochemistry in 187 LSCC patients. The potential association of tumor IDO expression with clinical parameters and tumor-infiltrating lymphocytes (TILs) was analyzed separately. Survival curves were estimated by the Kaplan-Meier method, and differences between groups were determined by log-rank test. Multivariate logistic regression analysis was performed to determine the independent factors associated with survival. Based on the evaluation score, 90 carcinomas (48.1 %) were identified with high IDO expression and 97 carcinomas (51.9 %) showed low expression. Tumor IDO expression was not associated with clinical stage, presence of metastases, and other clinicopathological parameters. Also, high IDO expression was not correlated with tumor-infiltrating CD3(+) and CD8(+) TILs. Instead it was positively related with the density of FOXP3(+) Tregs. Furthermore, multivariate analysis identified a significant association of overall survival and disease-free survival with tumor IDO status. IDO high expression represents a significant negative prognostic factor in patients with LSCC. Current results provide further support for using IDO as an immunotherapeutic target in LSCC. The precise role of tumoral IDO in human LSCC remains to be elucidated in the future.