BACKGROUND & OBJECTIVE: Obesity is a growing public health problem worldwide. Bariatric surgery is considered the safest and most effective therapeutic option, although it is associated with various metabolic and neurohormonal consequences. This study aims to evaluate the effect of sleeve gastrectomy (SG) on hypothyroidism within one year following surgery. METHODS: In this single-center prospective cross-sectional study, patients with morbid obesity who were candidates for SG were included. Body mass index (BMI), levothyroxine dosage, and thyroid function tests were compared at baseline and 12 months after surgery. RESULTS & CONCLUSION: Patients' BMI, levothyroxine dosage, TSH, and T4 levels decreased significantly after surgery (