Thyroid hypofunctional (“scintigraphic cool or cold”) nodules are detected frequently. Dependent on the clinical situation, on morbidity and on economic aspects it is necessary to select patients for sugery and to avoid unnecessary surgical treatment. Therefore it is necessary to develop appropriate diagnostic algorithm to manage hypofunctional thyroid nodules. The ultrasound guided fine-needle aspiration cytology (FNA) is on the one hand side a useful diagnostic tool, but on the other hand side there exist certain limitations. It is questionable if the nodule is correctly reached. In case of heterogeneous larger mixed nodules or multiple hypofunctional nodules, it is difficult to choose the correct location of punctation. Furthermore a certain number of FNA's is not diagnostic without any result or due to “follicular neoplasia”. 99m Tc-MIBI-sctintigraphy (MIBI) and 18 F-FDG-positron-emission-tomography (FDG-PET) are established methods in the follow-up of differentiated thyroid cancer after thyroidectomy with elevated thyroglobulin-levels without adequate 131-Iodine-uptake. Moreover in case of parafollicular medullary thyroid carcinomas after thyroidectomy with elevated calcitonin-concentrations the FDG-PET is a valuable diagnostic method in localizing tumor. However these tracers gain in importance in differentiating malignant from benign preoperative hypofunctional nodules. In conclusion MIBI-scintigraphy should be used routinely to plan the correct guide of FNA. The application of both methods (MIBI and FNA) improves the differentiation of dignity, whereas a negative MIBI-examination and a negative FNA is able to exclude malignancy nearly. In this way the number of unnecessary numbers of surgical treatments can be reduced. FDG-PET is not definitely superior compared to MIBI-scintigraphy. From the cost perspective MIBI is more attractive than FDG-PET.