Thyroid function may be reduced after treatment of cancer of the head and neck, and hypothyroidism is much more common after combination therapy. Whether hypoparathyroidism and subsequent hypocalcemia also occur after such treatment is unknown. Few related studies have been published in which changes in total serum calcium have been studied after cancer treatment with radioactive iodine or external radiation. Twenty-two disease-free head and neck cancer patients were studied, 1 to 3 years after multimodal treatment, to determine if changes in serum ionized calcium levels or thyroid function were present. Our results suggest that parathyroid function, as represented by ionized calcium levels remains normal after multimodality (surgery, radiation and/or chemotherapy) combined treatment.