Positron emission tomography (PET) is a powerful diagnostic nuclear medicine imaging technique. PET allows in vivo detection of a wide variety of physiologic and pathologic phenomena and it offers a noninvasive tool for the monitoring of therapy in various diseases. Invasive fungal infections (IFIs) are a global concern because of the increasing population of patients at risk of IFIs and the high morbidity and mortality. Therapy with antifungal agents is long-standing and expensive. The emerging resistant fungal strains make the management of IFIs challenging. There is an absolute need for a sensitive noninvasive biomarker capable of monitoring the disease activity of IFIs and determining the efficacy of treatment at an early time point. PET imaging with 18Ffluorodeoxyglucose (FDG) was used to detect and assess disease activity in IFI foci already over 20 years ago. At that time, it was suggested it could be a useful biomarker for monitoring antifungal therapy. However, this knowledge has still not been fully exploited for the management of IFIs. The literature reveals an increasing realization of the usefulness of PET in monitoring therapy of IFIs. In this review, we highlight the advantages of nuclear medicine techniques in the management of IFIs with emphasis of the role of PET in monitoring therapy efficacy.