The association between subclinical hypothyroidism (SCH) and cardiovascular risk, particularly with a TSH <10 µIU/ml, remains controversial. Aim and objectives: The aim of this study was to evaluate the changes in endothelial function and carotid artery intima-media thickness in patients with clinical and subclinical hypothyroidism. Subjects and methods: This study was a prospective study that was conducted on 150 Egyptian adults aged 18 to 50 years, recruited from endocrinology clinic at Kasr El-Ainy hospital during the period from March 2019 to April 2022. They were classified into the following three groups: Group (A): 50 patients with clinical hypothyroidism (CH group). Group (B): 50 patients with subclinical hypothyroidism (SCH group). Group (C): 50 euthyroid healthy subjects’ age and sex matched as control. Results: Regarding FMD, there is statistically significant difference in FMD among the three studied groups (P value < 0.001), CH and SCH groups had significant impairment in FMD compared to control group (P value < 0.001 & < 0.001 respectively), but there was no significant difference between CH and SCH groups (P value = 0.863). CIMT shows statistically significant difference among the three studied groups (P value < 0.001). Conclusion: CIMT was significantly increased in studied hypothyroidism patients than controls and, it was significantly higher in overt hypothyroidism compared to subclinical hypothyroidism. FMD is significantly impaired in CH and SCH patients compared to controls.