PURPOSE: Adrenocortical adenomas are common, whereas adrenocortical carcinomas are rare. Discriminating between benign and malignant adrenocortical tumors using conventional histology can be difficult. In addition, adrenocortical carcinomas generally have poor prognosis and limited treatment options. MicroRNAs are short noncoding RNAs that are involved in regulation of gene transcription. EXPERIMENTAL DESIGN: To identify microRNAs involved in the pathogenesis of adrenocortical tumors, expression profiling of microRNAs was done on a cohort of 22 adrenocortical carcinomas, 27 adrenocortical adenomas, and 6 normal adrenal cortices. RESULTS: Twenty-three microRNAs were found to be significantly differentially expressed between adrenocortical carcinomas and adrenocortical adenomas. miR-335 and miR-195 were significantly downregulated in adrenocortical carcinomas compared with adrenocortical adenomas. This result was further validated in an external cohort of six adrenocortical carcinomas and four adrenocortical adenomas. Using Kaplan-Meier analysis, downregulation of miR-195 and upregulation of miR-483-5p in adrenocortical carcinomas were significantly associated with poorer disease-specific survival. CONCLUSIONS: These findings indicate that deregulation of microRNAs is a recurring event in human adrenocortical carcinomas and that aberrant expression of miR-195 and miR-483-5p identifies a subset of poorer prognosis adrenocortical carcinomas. (Clin Cancer Res 2009;15(24):7684-92).