The rapid increase in CT use since 1990 and especially in the past 10 years has been accompanied by a coterminous worldwide increase in incidence of thyroid cancer especially in women. Are the two trends independent or related? Specific information from many countries and seven American states suggest that the relationship is real as no other cause can account fully for the temporal change in the frequency of this malignancy. Moreover, newer techniques of CT performance with or without the administration of iodinated contrast material favor the likelihood of a contingent association of image test utilization and thyroid cancer induction.