Fluorine-18 fluorodeoxyglucose (F-18 FDG) has been used to evaluate early-stage larynx cancer and metastases of thyroid cancer. However, elevated F-18 FDG uptake in laryngeal muscles may lead to misinterpretation. In this report, three patients with thyroid cancer are described who had thyroid surgery 2 months to 1 year before F-18 FDG positron emission tomographic imaging. Various degrees of moderate to intense uptake were observed in their laryngeal regions. In one patient, this was caused by laryngeal muscle uptake. To determine the origin of the increased muscle uptake in the other two patients, the authors analyzed the position and shape of the foci of high uptake in light of the patients' clinical histories and other imaging results.