OBJECTIVE: To describe outcome after thyroidectomy in hyperthyroid cats, with emphasis on peri- and postsurgical complications and recurrence. STUDY DESIGN: Retrospective study. ANIMALS: One hundred and one hyperthyroid cats. METHODS: Diagnostic work-up included preoperative measurement of plasma calcium, sodium, potassium, urea, and creatinine concentrations, and thyroid scintigraphy. A modified intracapsular dissection technique was performed. Postoperatively, parathyroid gland function was evaluated by measuring plasma calcium concentration several times daily. Outcome was obtained by standard telephone questionnaire. RESULTS: Thyroid scintigraphy revealed ectopic hyperplastic thyroid tissue (EHTT) in 9 cats. Preoperatively, 29 of 91 cats had hypokalemia. Two cats died within 3 days after surgery and 5 of 86 cats developed postoperative transient hypocalcemia. On histologic examination, thyroid carcinoma was identified in 3 of 88 cats. Hyperthyroidism recurred in 5 cats between 3 and 59 months; 4 of these cats had EHTT preoperatively. The difference in recurrence rate between hyperthyroid cats with and without EHTT was significant (P<.001). CONCLUSION: Complications were uncommon after thyroidectomy performed by an experienced surgeon when combined with an anesthetic regimen associated with minimal adverse cardiovascular effects. Hyperthyroid cats with EHTT had a significantly higher chance of recurrence. CLINICAL RELEVANCE: Thyroidectomy is associated with a low incidence of surgical complications and is an effective treatment for hyperthyroid cats when radioactive iodine therapy is not available. Preoperative thyroid scintigraphy is advised. Surgery is not recommended when EHTT is present, because of a higher chance of developing recurrent disease.