To elucidate the potential etiological role of RUNX3 in the development of salivary gland adenoid cystic carcinoma (ACC), we analyzed the methylation status of RUNX3 in a series of 114 ACC tissues and 3 ACC cell lines. Results showed that the methylated rate of RUNX3 was 50.9 and 3.5% in the 114 ACC samples and the corresponding normal salivary glands, respectively, achieving a significant difference (P<0.001). There was a significant correlation between RUNX3 methylation and various clinicopathological parameters of ACCs, such as perineural invasion, lymph node involvement, T-stage and distant metastasis (P<0.001). RUNX3 methylation was a significant predictor of the 5-year disease-free survival in ACC patients after surgery. Partial methylation was found in all 3 ACC cell lines, and the reactivation and more potent expression of RUNX3 was induced by 5-triazole-2-deoxycytidine. Our findings indicate that RUNX3 methylation may occur as a common event in the development of ACC and that methylation may be a major mechanism for inactivation of RUNX3 in ACC.