Background Data on the effects of excess aldosterone on glucose metabolism are inconsistent. This study compared the changes in glucose metabolism in patients with primary aldosteronism (PA) after adrenalectomy or treatment with a mineralocorticoid receptor antagonist (MRA). Methods Overall, 241 patients were enrolled; 153 underwent adrenalectomy and 88 received an MRA. Fasting glucose, homeostatic model assessment of insulin resistance (HOMA-IR), and homeostatic model assessment of β-cell function (HOMA-β) were compared between the treatment groups after 1 year. Plasma aldosterone concentration (PAC) and factors determining HOMA-IR and PAC were evaluated. Results No baseline differences were observed between the groups. Fasting insulin, HOMA-IR, and HOMA-β increased in both groups and there were no significant differences in fasting glucose following treatment. Multiple regression analysis showed associations between PAC and HOMA-IR (β=0.172, P=0.017) after treatment. Treatment with spironolactone was the only risk factor associated with PAC >30 ng/dL (odds ratio, 5.2; 95% confidence interval [CI], 2.7 to 10; P