Clinical oncologists have always shown great interest in circulating tumor markers. There are several markers that in the clinical routine are a signal of particular tumor types; some of them are strictly tissue-specific such as prostatic specific antigen (PSA) for prostatic cancer, AFP and HCG for germ cell tumors of the testis and ovary, others such as CA 15.3, CA125, CEA or cytokeratins are less specific since their elevations can be found in different varieties of cancers even if they are preferentially associated to a certain tumor type, thus are considered markers for breast, ovarian cancer and colon adenocarcinoma. The most useful clinical applications of these parameters is their determination during the follow-up of the treated patients, in order to detect the tumor recurrence early, and also to evaluate the evolution of the disease by monitoring the treatment responses. During follow-up, increasing levels of tumor markers can be observed even several months before the clinical demonstration of cancer recurrence. The association of tumor marker tests with imaging modalities can lead to several advantages: the first is to confirm the diagnosis of relapses, possibly before the appearence of the related clinical symptoms due to tumor growth; the second is to localize the sites of lesions, while tumor markers provide only a general indication of the existence of metastases; the third is to make possible a correct whole body restaging. In the assessment of cancer response tumor markers are often very reliable and their changes are faster than the morphological ones. Among all the imaging modalities, nuclear medicine plays an important role in detecting recurrences and metastatic localizations as it is able to investigate functional rather than morphological aspects of tumors, and provide different information in comparison to morphologic imaging. In addition, the scintigraphic techniques offer the possibility to evaluate treatment responses, confirming or not the information from biochemical changes. This review aims to show some examples (breast, prostate and ovarian cancer) in which the combination of nuclear medicine imaging modalities and tumor marker tests is proposed for clinical practice. The advantages and some critical aspects are discussed on the basis of the clinical findings and the most important clinical indications are described.