A 52 year-old woman with gastric cancer treated with surgery and chemotherapy, is admitted in our Internal Medicine Department because of the presence of fever (max 41.2 degrees C), dyspnoea, non-productive cough and mental confusion. The anamnesis and the physical examination address to the diagnosis of CAP (Community-Acquired Pneumonia); in particular the alteration of consciousness and the onset of symptoms after the insertion of a nose-gastric tube let us to consider the diagnosis of aspiration pneumonia. The clinical presentation and radiological imaging (Rx and CT of thorax) suggest the pattern of bronchiolitis obliterans with organizing pneumonia (BOOP). BOOP is not a disease, but a non specific pattern of answer to a lung injury. It can be either idiopathic or associated with a variety of causes, such as infections, drugs, radiations and connective tissue diseases. Besides the clinical course is complicated by the onset of an ARDS (Adult Respiratory Distress Syndrome). The gold standard for the diagnosis is represented by lung biopsy with hystopathologic confirmation but, if it cannot be done, it's necessary to start immediately steroid therapy because BOOP may be fatal. The patient received antibiotic and steroid therapy with success.