In Hodgkin's lymphoma (HL), PET imaging should be performed in all patients, particularly in stage I or II disease where change in staging will alter management. For aggressive Non-Hodgkin's lymphoma (NHL), PET imaging is valuable to provide a baseline for response evaluation. For indolent NHL, it is concluded that PET imaging is not generally indicated. For HL, a negative FDG-PET scan is highly indicative of long-term, disease-free survival and is particularly useful in the presence of residual CT mass. For aggressive NHL, a positive FDG-PET scan is predictive of disease persistence or recurrence. There is a significant incidence of false-negative FDG-PET scans, which in most cases means minimal residual disease that cannot be detected by the current instrumentation. For both NHL and aggressive HL, early assessment of response appears to be predictive of long-term outcome. Optimal time of FDG-PET scan during therapy needs to be determined. For indolent NHL, the high rate of false-negative FDG-PET scans raises questions to its clinical role in response evaluation. FDG-PET and PET-CT improve primary staging and restaging of lymphomas. Metabolic imaging will be the standard technology for assessment of therapy with documented prognostic value. Imaging during therapy may be valuable to individualize therapeutic protocols and to define chemosensitivity of tumor tissue. Minimal residual disease cannot be detected with current imaging devices.