To describe a fatal case of influenza A pneumonia in a patient with severe lymphopenia after receiving subcutaneous cladribine to treat her multiple sclerosis (MS). Case report. A 53-year-old woman developed fatal influenza pneumonia associated with grade 4 lymphopenia two months after receiving a total dose of 60mg subcutaneous cladribine. Despite treatment with oseltamivir, her condition deteriorated and the patient passed away after developing respiratory failure. Cladribine-related lymphopenia is usually mild to moderate, however severe lymphopenia may occur. People with MS, especially those who are immunosuppressed, should be offered the inactivated influenza vaccine annually.