A 35-year-old woman with Crohn s disease who was receiving long-term immunosuppressive therapy with azathioprine developed a primary cytomegalovirus (CMV) infection, likely transmitted by her son after he started attending kindergarten. The infection took a severe course, characterized by a high viral load, sepsis, and subsequent CMV pneumonitis requiring mechanical ventilation. The patient was successfully treated with intravenous ganciclovir to which she responded favorably. At a follow-up three months after discharge, she was in good clinical condition, with no pathological findings on a high-resolution CT scan of her lungs. This case highlights the risk of severe primary CMV infection in immunosuppressed patients and underscores the importance of early diagnosis and appropriate antiviral therapy. Keywords: cytomegalovirus, primary infection, immunosuppression, sepsis, pneumonitis, ganciclovir.