Object: This comparative study clarified the clinical characteristics and in vitro steroidogenic activities of aldosterone-producing adenomas (APAs) harboring ATPase or CACNA1D gene mutations. Design and Patients: Genetic testing was performed on 159 unilateral APAs. Somatic ATPase and CACNA1D gene mutations were analyzed in 42 APA tissues without KCNJ5 gene mutations. Results: ATP1A1, ATP2B3, and CACNA1D mutations were detected in one, four, and four patients, respectively. Compared with patients without KCNJ5, ATPase, or CACNA1D mutations (wild type), ATPase mutations tended to have more severe hyperaldosteronism and smaller tumors; those with CACNA1D mutations had clinical characteristics and tumor sizes similar to those with wild-type genes. APAs with ATPase mutations were composed mainly of compact eosinophilic tumor cells, whereas CACNA1D mutations resulted in predominantly clear tumor cells. Aldosterone production in APA cells with ATP2B3 mutations were more responsive to dibutyryl cAMP, whereas those with CACNA1D mutations were more responsive to adrenocorticotropic hormone than the wild-type cells. Conclusion:APAswith ATPase mutations demonstrated a potentially severe primary aldosteronism phenotype, whereas those with CACNA1D mutations displayed characteristics similar to wild-type APAs. The status of stimulated aldosterone production was also different accorDing to the cell types, suggesting that the regulatory effects of adrenocorticotropic hormone on aldosterone synthesis could possibly vary accorDing to the intracellular signaling involved in hormone production.