Studies have shown that aberrant expression of IL‐12p40, which is encoded by the interleukin‐12B (IL‐12B) gene, may be involved in the development of endometriosis. In this study, we investigated the role of aberrant methylation of the
IL‐12B promoter region and its associated expression in the development of ovarian endometriosis. By using pyrosequencing, we analyzed the methylation level of the
IL‐12B promoter region in eutopic and ectopic endometrium of patients with ovarian endometriosis and normal endometrium of control women. The expression of
IL‐12B mRNA was detected by quantitative real‐time PCR. The results showed that the methylation level of the
IL‐12B promoter region in ectopic and eutopic endometrium of patients with ovarian endometriosis was significantly lower than that in endometrium of women without endometriosis (
p < 0.001 and
p = 0.041, respectively). In contrast, mRNA levels were significantly increased in ectopic and eutopic endometrium of patients with ovarian endometriosis compared to those in endometrium of women without endometriosis (
p < 0.001 and
p = 0.042, respectively). Correlation analysis showed that the methylation level of the
IL‐12B promoter region was negatively correlated with mRNA levels of
IL‐12B (
p < 0.001). Our data suggested that aberrant methylation of the
IL‐12B promoter region may be responsible for aberrant
IL‐12B mRNA expression in endometrium tissue of women, which may be associated with the development of ovarian endometriosis in northern Chinese women.