An ideal marker for bacterial infections should allow an early diagnosis, inform about the course and prognosis of the disease and facilitate therapeutic decisions. Procalcitonin (ProCT) covers these features better as compared to other, more commonly used biomarkers, and thus, the current hype on ProCT has a solid scientific basis. A superior diagnostic accuracy of ProCT has been shown for a variety of infections, eg respiratory tract infections, meningitis, acute infectious endocarditis and pancreatitis. Importantly, a ProCT-based therapeutic strategy can safely and markedly reduce antibiotic usage in lower respiratory tract infections, the major cause of sepsis. Being a hormokine mediator, immunoneutralisation of ProCT might offer new hope for more effective treatment options in sepsis. It is now evidence-based that ProCT provides more information and, thereby, questions the currently used "gold standards" for the diagnosis of clinically relevant bacterial infections. Yet, ProCT is less than a perfect marker. ProCT can be increased in non-infectious conditions, and may remain low in infections. The diagnosis of bacterial infections will continue to require a critical clinical awareness, careful patient history, dedicated physical examination, and appropriate cultures. This review aims to help the clinician to understand the physiopathological basis, to appreciate strengths and weaknesses of this biomarker, and thereby to promote a rational implementation of ProCT in a routine setting.