Adrenocortical carcinoma is a rare endocrine tumor with a poor prognosis. These tumors can be diagnostically challenging, and diagnostic algorithms and criteria continue to be suggested. Myxoid and oncocytic variants are important to recognize to not confuse with other tumors. In addition, the diagnostic criteria are different for oncocytic adrenal carcinomas than conventional carcinomas. Adrenocortical carcinomas usually occur in adults, but can also occur in children. In children these tumors are diagnostically challenging as the histologic features of malignancy seen in an adult tumor may not be associated with aggressive disease in a child. Adrenocortical carcinomas occur with increased frequency in Beckwith-Wiedemann and Li-Fraumeni syndromes, but most occur sporadically. Gene expression profiling by transcriptome analysis can discriminate adrenocortical carcinomas from adenomas and divide carcinomas into prognostic groups. The increasing understanding of the pathogenesis of these tumors may provide increasing treatment targets for this aggressive tumor.