We describe the case of a 56 years-old man with a subacute onset of symptoms mimicking a granulomatosis with polyangiitis. He was admitted to our hospital with acute respiratory failure requiring oxygen therapy, fever and crusted rhinitis. Despite initial improvement in radiological and clinical features with a steroids therapy, his condition worsened rapidly and he was re admitted to our department with ARDS. Despite antibiotic, antiviral and antifungal therapy, an endotracheal intubation was necessary and ultimately the patient passed away. Only a histological examination on autopsy had shown the presence of a diffuse Anaplastic Large Cell Lymphoma (ALCL), a rare type of non-Hodgkin lymphoma (NHL) originated from mature post-thymic T cells. It represents 1–3% of NHL. Different subtypes have been described: Kinase (ALK)-negative ALCL, ALK-positive ALCL and breast implantassociated ALCL. ALK-negative ALCL affects mainly old males and has the worst prognosis.