The Ras association domain family (RASSF) encodes for distinct tumor suppressors and several members are frequently silenced in human cancer. In our study, we analyzed the role of a novel RASSF member termed RASSF10 in thyroid carcinogenesis. The RASSF10 CpG island promoter was intensively methylated in nine thyroid cancer cell lines and in 66% of primary thyroid carcinomas. RASSF10 methylation was significantly increased in primary thyroid carcinoma compared to normal thyroid and follicular adenoma (0 and 10%, respectively; p < 0.004). Patients with cancerous lymph nodes were significantly hypermethylated for RASSF10 in primary thyroid tumors compared to those with non-affected lymph nodes (79 vs. 36%; p = 0.047). RASSF10 promoter hypermethylation correlated with a reduced expression and treatment with a DNA methylation inhibitor reactivated RASSF10 transcription. In summary, our data show frequent epigenetic inactivation of RASSF10 in thyroid cancer. These results suggest that RASSF10 may encode a novel epigenetically inactivated candidate tumor suppressor gene in thyroid carcinogenesis.