Abstract Context Primary aldosteronism (PA) represents the most frequent form of endocrine hypertension. Hyperaldosteronism and hypercortisolism both induce excessive left ventricular hypertrophy (LVH) compared with matched essential hypertensives. In recent studies frequent cosecretion of cortisol and aldosterone has been reported in patients with PA. Objective Our aim was to investigate the impact of cortisol cosecretion on LVH in patients with PA. We determined 24-hour excretion of mineralocorticoids and glucocorticoids by gas chromatography–mass spectrometry and assessed cardiac remodeling using echocardiography initially and 1 year after initiation of treatment of PA. Patients We included 73 patients from the Munich center of the German Conn’s registry: 45 with unilateral aldosterone-producing adenoma and 28 with bilateral adrenal hyperplasia. Results At the time of diagnosis, 85% of patients with PA showed LVH according to left ventricular mass index [(LVMI); median 62.4 g/m2.7]. LVMI correlated positively with total glucocorticoid excretion (r2 = 0.076, P = 0.018) as well as with tetrahydroaldosterone excretion (r2 = 0.070, P = 0.024). Adrenalectomy led to significantly reduced LVMI in aldosterone-producing adenoma (P < 0.001) whereas mineralocorticoid receptor antagonist therapy in bilateral adrenal patients with hyperplasia reduced LVMI to a lesser degree (P = 0.024). In multivariate analysis, the decrease in LVMI was positively correlated with total glucocorticoid excretion and systolic 24-hour blood pressure, but not with tetrahydroaldosterone excretion. Conclusion Cortisol excess appears to have an additional impact on cardiac remodeling in patients with PA. Treatment of PA by either adrenalectomy or mineralocorticoid receptor antagonist improves LVMI. This effect was most pronounced in patients with high total glucocorticoid excretion.