Adrenal gland diagnostics can pose significant challenges. In most academic and community practice settings, adrenal gland resections are encountered less frequently than other endocrine or genitourinary specimens, leading to less familiarity with evolving classifications and criteria. The unique dichotomy between cortical and medullary lesions reflects the developmental evolution of these functionally independent components. Adrenal cortical lesions at resection include hyperplasia, adenoma, and carcinoma, with some cases straddling the boundary between these distinct clinical classifications. The lack of immunohistochemical or molecular markers to definitively categorize these intermediate lesions enhances the diagnostic challenge. In addition, modified terminology for oncocytic and myxoid cortical lesions has been proposed. Medullary lesions are somewhat easier to categorize; however, the prediction of aggressive behavior in pheochromocytomas remains a challenge due to a lack of reliable prognostic biomarkers. Recent work by the Cancer Genome Atlas Project and other research groups has identified a limited subset of molecular and signaling pathway alterations in these 2 major neoplastic categories. Ongoing research to better define prognostic and predictive biomarkers in cortical and medullary lesions has the potential to enhance both pathologic diagnosis and patient therapy.