Background : Hypothyroidism is a syndrome caused by the diminished level of thyroid hormones. Its prevalence has been reported 1-8% in adequate-iodine and 10-20% in low-iodine level regions. The present study has determined the epidemiology of hypothyroidism in Gilan.

Materials and methods : For this retrospective study, demographic data of ELISA-documented patients with hypothyroidism were gathered during a 10-year period. SPSS soft ware was use for data analysis.

Results : Of 407 patients, 84% were females. The mean age of females and males were 37.9±14.8 and 39.5±17 years. Hashimoto was by far the most common cause. Fatigue and weakness were the most common symptoms. All patients had goiter of 1^st to 3^rd degree.

Conclusion : Results have revealed that hypothyroidism is a common complaint in 40-60 years old females. Thyroid tests should be performed in high risk population.