© 2021 Ankara Yildirim Beyazit University. All rights reserved.Objectives: We aimed to evaluate adherence and determine the factors that are related to adherence in patients on levothyroxine therapy. Materials and Methods: Patients older than 18 years old and using levothyroxine for primary hypothyroidism were recruited. Demographical and clinical features, practices of using levothyroxine, and compliance were evaluated through a questionnaire. Those who answered the frequency of not using/skipping the drug as never/rarely, sometimes, and frequently/often were grouped as high, medium, and low adherence, respectively. Results: Data of 335 patients -282(84.18%) female and 53(15.82%)- male, with a mean age of 47.36±12.50 were analyzed. 330 (98.50%) patients were taking levothyroxine in the morning, and 332 (99.10%) were taking fast. 8(%2.41) patients were taking the drug just before the meal, and 66(19.88%) were taking it in 15 minutes. 66.66% of 145 patients using a medication that interferes with the absorption of levothyroxine were using it less than 2 hours of levothyroxine. There were 218 (65.08%) high, 98 (29.25%) medium and 19 (5.67%) low adherence patients. Drug adherence was not associated with demographical features, the cause and duration of hypothyroidism, the presence of comorbid disease, and thyroid hormones. Higher education level and familial thyroid disease were associated with high adherence (p=0.008 and p=0.013, respectively). Conclusion: Drug adherence was medium/ low in 34.92% of hypothyroid patients. A considerable amount of patients did not leave enough time between levothyroxine and meal or other medications. For effective treatment of hypothyroidism, it is important to inform patients about hypothyroidism and levothyroxine use and increase drug compliance.