Primary adrenal insufficiency (PAI) consists in a lack of adrenal hormones, and particularly of cortisol and aldosterone. It typically presents with fatigue, weakness, loss of appetite, increased thirst and skin hyperpigmentation. While most cases stem from an autoimmune etiology, rare instances of PAI have been attributed to infection, adrenal hemorrhage and medication disrupting steroidogenesis pathways. This report presents two patients with hematologic malignancies who developed primary glucocorticoid deficiency due to posaconazole. Both received allogeneic stem-cell transplantation and used posaconazole as antifungal prophylaxis. Both patients had low morning cortisol and elevated ACTH levels, which suggested primary adrenal insufficiency. Posaconazole, widely used for antifungal prophylaxis and long-term therapy, undoubtedly affects adrenal steroid synthesis. Thus, healthcare providers must be aware of that posaconazole may cause adrenal insufficiency, and should monitor patients taking this medication.