Objectives: The expression of steroidogenic factor-1 (SF-1) was elevated in adrenal aldosterone-producing adenoma (APA). The influence of SF-1 on adrenal tumorigenesis by adrenocortical cell line H295R cells was investigated. Materials and methods: Real-time PCR and Western blotting were used to detect SF-1 expression in 16 APA samples and 12 normal adrenal samples. Specific SF-1-shRNA plasmid was transfected into H295R cells to inhibit SF-1 expression. Western blotting and real-time PCR were used to verify the effects of RNAi on SF-1 inhibition. Subsequently, WST-1 and cell count were applied to evaluate cell proliferation at different SF-1 levels. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was used to measure cell apoptosis, and proliferation marker Ki-67 was studied by immunohistochemistry. Results: Compared with normal adrenal samples, SF-1 mRNA and protein levels in APA samples were significantly higher. It was 10.48:1 at SF-1 mRNA and 0.87 +/- 0.05 vs. 0.39 +/- 0.07 at protein levels, respectively (P < 0.01). A decreased SF-1 significantly inhibited cell proliferation in the experimental and control cells. These results were supported by weaker Ki-67 staining in SF-1-inhibited cells [(36.9% +/- 4.17%) vs. (58.48% +/- 7.16%) (P < 0.01)]. Moreover, SF-1 inhibition induced a 2.7-fold increase in the percentage of apoptotic H295R cells (P < 0.01). Conclusions: Elevated SF-1 may play an important role in APA formation and primary aldosteronism. SF-1 acts as an oncogenic factor, and its inhibition provides new insight into the understanding and treatment of related adrenal diseases. (C) 2012 Elsevier Inc. All rights reserved.