Aims: Thyroid hormones T3/T4 participate in the fine tuning of development and performance. The function and growth of thyroids depends on K⁺ channels establishing the electrochemical gradient across the cell membrane. The present paper explored whether KCNQ1, a widely expressed voltage gated K⁺ channel, participates in the regulation of thyroid function. Methods: KCNQ1 transcript and protein abundance have been determined utilizing RT-PCR and confocal immunohistochemistry. Thyroid function has been analyzed in KCNQ1 deficient mice (kcnq1^-/-) and their wild type littermates (kcnq1^+/+). Results: KCNQ1 transcripts were abundant in thyroid gland tissue and KCNQ1 protein is expressed in follicular cells of the thyroid gland. Despite a tendency of TSH plasma concentrations to be higher in kcnq1^-/- than in kcnq1^+/+ mice, the thyroid mass, T3 and T4 plasma concentrations were significantly lower in kcnq1^-/- than in kcnq1^+/+ mice. Moreover, body temperature was significantly higher in kcnq1^-/- than in kcnq1^+/+ mice. In conclusion, KCNQ1 is required for proper function of thyroid glands.