Abstract Background Posaconazole is an extended-spectrum triazole used in the treatment and prophylaxis of many fungal diseases. There have been case reports of posaconazole-induced pseudohyperaldosteronism; however, its occurrence and association with serum posaconazole drug levels need further investigation. Methods In this single-center retrospective observational study, we examined the occurrence of posaconazole-induced pseudohyperaldosteronism (PIPH), diagnosed either clinically or via laboratory abnormalities, and evaluated differences in serum posaconazole concentration and clinical characteristics between those with and without this syndrome. Results Sixty-nine patients receiving posaconazole were included; of whom, 16 (23.2%) met the definition of PIPH. Patients with PIPH were significantly older (61.1 vs. 44.7 years, P = 0.007), more frequently had hypertension prior to starting posaconazole (68.8% vs. 32.1%, P = 0.009), and were more frequently prescribed posaconazole for active treatment instead of prophylaxis compared with patients without PIPH (62.5% vs. 24.5%, P = 0.005). Patients with PIPH had a significantly higher median serum posaconazole level than those without PIPH (3.0 vs. 1.2 µg/mL, P = 0.0001). There was a positive correlation between serum posaconazole level and change in systolic blood pressure (r = 0.37, P = 0.01), a negative correlation between serum posaconazole level and change in serum potassium (r = −0.39, P = 0.006), and a positive correlation between serum posaconazole level and serum 11-deoxycortisol (r = 0.69, P < 0.0001). Conclusion Posaconazole is associated with secondary hypertension and hypokalemia, consistent with pseudohyperaldosteronism, and development is associated with higher serum posaconazole concentrations, older age, and baseline hypertension. Management may include dose reduction, the addition of an aldosterone antagonist, or an alternative triazole agent. Disclosures All authors: No reported disclosures.