Thyroid disorders represent the second most common endocrine disorder after diabetes mellitus. For this reason, investigation of thyroid function is frequently carried out, taking advantage of numerous tests currently available. It it the physicians's difficult task to select the most appropriate assay(s) in the different pathophysiological conditions from the bewildering array of thyroid function tests, in order to satisfy optimal diagnostic standards, but also to fulfill cost/benefit criteria. Aim of this paper is to provide a brief overview of advantages and disadvantages of main thyroid function tests, and to suggest a testing strategy for the diagnosis of suspected thyroid dysfunction.