Persistent pneumonias are frequent both in hospital and primary care settings. Several parameters have to be taken into account. Firstly the appropriateness of treatment; secondly the immune status of the host; and finally infectious complications need to be ruled out. Several non-infectious diagnoses can mimic a persistent infiltrate, such as neoplastic disorders, organising pneumonias, interstitial disorders and drug - or radiation-induced lung diseases. Uncommon pathogens will not respond to common treatment, for instance atypical bacteria, mycobacteria, fungi including Pneumocystis as well as viruses. Referral to a pulmonologist should be considered to perform a fiberoptic bronchoscopy.