Cryptogenic Organising Pneumonia (COP) is a relatively rare condition and can be difficult to differentiate from Community acquired pneumonia (CAP). We report two cases which demonstrate the importance of considering this differential diagnosis in patients with spontaneous pneumothorax who have raised inflammatory markers or lung infiltrates. Our report highlights the value of serum procalcitonin as a biomarker in differentiating between community acquired pneumonia and cryptogenic organising pneumonia especially in the context of a high serum C-reactive protein. Furthermore, the cases show early diagnosis and prompt treatment with corticosteroids may impact the clinical outcome.