Non-resolving pneumonia is a common clinical problem that prolongs morbidity and increases hospitalization costs. We report an 82 year-old non-smoking female who was admitted with chronic diarrhea and later developed nosocomial pneumonia. Lung infiltrates did not resolve despite sequential antibiotic treatments. Infectious causes such as resistant nosocomial pathogens, respiratory viruses, tuberculosis, Legionellosis, cytomegalovirus or agents associated with HIV infection were discarded. Non-infectious causes such as thromboembolic lung disease, neoplasms and rheumatic disorders were also ruled out. An exudative pleural effusion was detected, but the study was unremarkable. Fiberoptic bronchoscopy and a transbronchial biopsy, revealed nonspecific findings. The patient persisted febrile, required non-invasive mechanical ventilation and displayed a migratory pattern of lung infiltrates that motivated a second biopsy, this time by open thoracotomy, showing a cryptogenic organizing pneumonia. The patient's conditions improved after treatment with adrenal steroids. In patients with non-resolving pneumonia, a dedicated and comprehensive study should be done using invasive procedures and considering both infectious and non-infectious causes. Cryptogenic organizing pneumonia is one of the alternatives that is potentially treatable, but often underdiagnosed.