To study the mRNA expression of the tumor suppressor gene thyroid stimulating hormone receptor (TSHR) gene in papillary thyroid carcinoma (PTC) and the correlation between aberrant promoter methylation of TSHR gene and the tumorigenesis of PTC.RT-PCR was used to detect the mRNA expression of TSHR gene in 50 PTC cases, 20 cases of nodular goiter and 12 cases of thyroid adenoma tissue. The status of TSHR gene promoter methylation was determined using methylation-specific PCR technique.Of the 50 PTC patients, 34 (68%) were found to have hypermethylation of TSHR gene promoter region, as compared to 7 out of the 32 control patients (21.9%) positive for TSHR gene promoter hypermethylation, suggesting a significantly higher rate of TSHR promoter methylation of in PTC patients than in the control patients (chi(2) = 16.61, P<0.05). Of the 34 PTC patients with TSHR promoter methylation, 14 (41.2%) showed the absence of TSHR mRNA expression; in the 16 PTC patients without TSHR promoter methylation, only 2 (12.5%) were negative for TSHR mRNA expression, showing a significant difference in the rate of negative TSHR mRNA expression with regard to TSHR promoter methylation. The PTC patients had a significantly lower TSHR mRNA expression than the control patients (chi(2) = 4.02, P<0.05).Methylation of TSHR gene in the promoter region is a common molecular event, which might be associated with the tumorigenesis and progression of human PTC.