Activin affects adrenocortical steroidogenesis and increases apoptosis, while follistatin (FS) acts as an activin antagonist by binding to activin, preventing attachment to its receptors. The regulation of FS expression in the adrenal cortex is poorly understood. Adrenocortical tumors often display aberrant methylation. In the present study, we investigated the effect of DNA methylation on FS mRNA expression and peptide secretion in adrenocortical cells. We treated human NCI-H295R adrenocortical cells with the methylation inhibitor 5-Aza-2′deoxycytidine (Azad; 0.1–100 μM for 1, 4 or 7 days) and measured FS mRNA expression by Northern blot and quantitative real time RT-PCR analyses as well as FS secretion by specific ELISA. Methylation-specific PCR showed decreased methylation in the FS promoter region after Azad treatment. A significant (P < 0.05) time- and dose-dependent increase in FS mRNA expression (up to 4.6-fold) and peptide secretion (up to 17.1-fold) was detected after Azad treatment. We conclude that FS gene expression and peptide secretion in NCI-H295R adrenocortical cells are regulated by DNA methylation. Thus, variable methylation in different adrenocortical tumors may influence activin bioactivity and its consequences in steroidogenesis and cell proliferation/apoptosis.