Lymphomas have represented an indication for nuclear medicine investigations for 30 years. Gallium-67 scintigraphy has been shown to be a valuable complementary method in Hodgkin's disease and non-Hodgkin lymphoma for detecting viable residual lesions after chemotherapy and for diagnosis of a relapse. Thallium-201 is of interest in differentiating cerebral lymphomas from infectious lesions in AIDS patients but less useful in extra-cerebral lymphomas. PET with fluorine-18-FDG is more accurate than 67Ga in lymphoma. In patients with a positive PET scan after chemotherapy an early relapse occurs in up to 100%, while more than 80% of patients with a negative PET will have a long-term remission. Most studies show that FDG-PET is significantly correlated with patient outcome whereas there is much weaker or even no correlation for CT. The main reason is that PET is not bound to morphological criteria like lymph node size while CT is often not able to differentiate between residual tumour and post-therapeutic fibrosis. Therefore, based on a considerable number of clinical studies, FDG-PET gains increasing significance for staging, restaging and therapy monitoring in malignant lymphomas.