A 16-year-old girl with a rare immune system disorder called chronic granulomatous disease developed a serious fungal infection caused by Rasamsonia argillacea, a fungus that is not commonly seen in clinical practice. The infection presented as a painful collection in her chest wall that required surgery and multiple antifungal medications. This is the first reported case of this particular fungal infection in the Arabian Peninsula, and successful treatment required a combination of drugs chosen based on laboratory testing of the fungus’s resistance patterns.