The suspicion of a serious condition arises if a smoker is coughing and losing weight constantly. Serology and imaging are great options for diagnosis, but what is their specificity? A 62-year-old man presented with persistent cough, weight loss and hypoxia. A chest x-ray revealed bilateral interstitial infiltrates. Treatment with several antibiotics failed. Serological results showed antineutrophil cytoplasmic antibodies (c-ANCA) positivity. However, biopsy result indicated cryptogenic organising pneumonia. This case report discloses the differential diagnosis of c-ANCA positive interstitial lung disease in detail.