CNS infections caused by infective agents are rare in immunocompetent hosts, but more frequent in immunocompromised patients. In addition, the spectrum of causative agents is completely different. There are no pathognomonic alterations in radiologic imaging, even in clinically severely ill patients imaging is often non-specific or inconspicious. This article gives a review of the most frequent infective agents and image alterations. Modern radiology is not yet able to replace the gold standard of pathogen detection.