The objective was to examine changes in trace elements due to thyroid cancer in humans. Serum levels and tissue contents of trace elements (Zn, Cu, Mn, Mg, Fe and Se) were measured in 43 patients with thyroid cancer before and 4 days after surgery were compared to normal values. The serum levels of zinc in cancer patients were lower than those of normal subjects. Surgical removal of the cancer resulted in the restoration of these levels. Although serum Cu levels in patients were not different from normal, but post-operatively these levels rose significantly (p < 0.001). Levels of Fe, Mg and Mn were significantly lower (p < 0.001) post-operatively. There was no significant change in Serum Se levels. The thyroid tissue contents of these trace elements did not show a difference between the normal (Juxta-tumor) thyroid tissue and the cancerous lesion. Out of the six trace elements examined, the decrease of serum levels of zinc in cancer patients may be linked to the disease condition. It is suggested that this change: (a) may be used to demonstrate successful cancer surgery and (b) may have implications for a long-term follow-up of thyroid cancer patients.