Identify criteria and create a risk scoring system to predict hypothyroidism after hemithyroidectomy. We have retrospectively studied 216 cases of patients with goiter who had undergone hemithyroidectomy from January 2002 to December 2007 at Vilnius University Hospital Santariškių Klinikos. Patients were divided into two groups according to their thyroid function after hemithyroidectomy: 168 (77.8%) patients’ thyroid function was normal (group A), 48 (22.2%) patients had symptoms of hypothyroidism (group B). The relationship between groups and parameters such as patients’ sex, age, patient’s weight, preoperative serum thyroid-stimulating hormone (TSH) level, weight of the remnant gland, ratio of the remaining thyroid gland weight to patient’s weight was statistically analysed. The patients’ mean age was 41.6 ± 14.1 years in group A and 52.9 ± 13.9 years in group B (p=0.0002). The mean preoperative TSH level was 0.79 ± 0.5 mU/L in group A, compared with 1.42 ± 1.00 mU/L in group B (p= 0.005). The mean ratio of the remaining thyroid gland weight to patient’s weight was 0.102 ± 0.053 g/kg in group A and 0.063 ± 0.027 g/kg in group B (p=0.04). The groups did not establish a significant difference between patients’ sex, patient’s weight or weight of the remaining gland. Patient’s age, preoperative serum TSH level, ratio of the remaining thyroid gland weight to patient’s weight is the main factors of hypothyroidism after hemithyroidectomy. A risk scoring system was created to predict hypothyroidism after hemithyroidectomy before the operation.