In the past decade, our knowledge of neoplasms arising in the adrenal cortex has been expanded greatly. Histologic criteria for distinguishing benign from malignant adrenal cortical neoplasms have been developed. In this review, three systems useful in making this distinction are reviewed and compared. Pathologic indicators of prognosis for adrenal cortical carcinomas have been proposed and these include mitotic rate, stage, surgical resectability, nuclear grade, and tumor size. Of these, mitotic rate appears to be the best indicator. Adrenal cortical carcinomas with a high mitotic rate behave most aggressively. The role of immunohistochemical and DNA content analysis in the diagnosis of adrenal cortical neoplasms is limited. Neoplastic adrenal cortical cells contain a low density of keratins that is often destroyed by routine fixation and paraffin embedding. Thus, the absence of keratins in adrenal cortical neoplasms, particularly carcinomas, in routinely processed tissue should not dissuade the pathologist from making the diagnosis of an epithelial neoplasm. DNA content analysis has revealed an imperfect correlation between DNA ploidy and histologic diagnosis. Some adrenal cortical adenomas contain aneuploid stem cell lines, whereas some adrenal cortical carcinomas have diploid DNA content. Molecular genetic analyses suggest that one or more tumor suppressor genes may be involved in the pathogenesis of adrenal cortical neoplasms.