We investigated expression levels of Nicotinamide N-Methyltransferase (NNMT), an enzyme involved in the biotransformation of many drugs and xenobiotic compounds, in oral squamous cell carcinoma (OSCC). Measurements were performed by immunohistochemistry and the relationship between tumour characteristics and NNMT levels in OSCC was studied to evaluate the effectiveness of NNMT as a prognostic marker in squamous cell carcinoma of the oral cavity. In conclusion, the present study suggests that NNMT may have potential as a biomarker and as a therapeutic target for OSCC.