This overview presents the indications of tumour SPECT in contrast to tumour PET using (18)F-FDG. A number of diagnostic SPECT radiopharmaceuticals have been used for years in oncology and are widely available in nuclear medicine departments. Today, tumour SPECT has to compete with tumour PET using (18)F-FDG. Other PET radiopharmaceuticals are common only in specialised centers. In comparison to SPECT, PET images with their higher resolution are technically superior. Therefore, PET is better than SPECT in localising a tumour, if the special tumour entity accumulates (18)F-FDG. Thus, (18)F-FDG-PET has largely replaced SPECT examinations using (201)Tl chloride, (67)Ga citrate or (99m)Tc anti-CEA. It is questionable whether mammascintigraphy using (99m)Tc-MIBI or (99m)Tctetrofosmine will be broadly accepted in clinical routine. SPECT radiopharmaceuticals are still up to date for examination of tumour entities which do not accumulate (18)F-FDG (e. g. neuroendocrine tumours) and in clinical problem solving if (18)F-FDG-PET is not regarded as superior (e. g. search for recurrent medullary thyroid carcinoma) or in the management of tumours with overlapping diagnosis and therapy as it is the case for differentiated thyroid carcinomas ((123)I/(131)I-NaI), phaeochromozytomas, and neuroblastomas ((123)I/(131)I-MIBG), carcinoids, gastroenteropancreatic tumours, paragangliomas, and Merkel-cell tumours (somatostatin receptor scintigraphy). Future developments concerning new SPECT radiopharmaceuticals and image fusion such as SPECT/CT are expected.