(18)F-FDG-PET is a well established standard procedure for most lymphoma subtypes. In particular the advantage of metabolic imaging stands in its strong predictivity in response. Indeed PET scan has been incorporated into revised response criteria for aggressive lymphomas and recommended to be performed at baseline and after therapy. At the same time, several ongoing clinical trials are investigating the value of treatment adaptation based on interim PET (PETi) results for Hodgkin Lymphoma (HL) and aggressive Non-Hodgkin Lymphoma (NHL). On the other hand, scientific literature provides limited detailed information regarding the numerous non aggressive NHL subtypes. Usually indolent NHL are typically less FDG avid, furthermore their long natural history and high incidence of recurrence decreases the clinical impact of a potential risk-adapted or response-adapted approach. We reviewed, from a nuclear medicine point of view and a clinical point of interest, evidence for the use of FDG-PET in monitoring early and end treatment response.