This study was a cross-sectional study run among 2417 of the general population from different areas of Saudi Arabia, aiming to determine the prevalence as well as the risk factors of hypothyroidism, and its relationship with diabetes mellitus. A multistage random sampling technique has been followed. For data collection, we used a pre-designed online-disseminated questionnaire. Our study found that 18.7% of the study population had hypothyroidism, most of whom (86.3%) were females. Sense of lethargy and laziness was found in 72.9%, dryness of the skin in 71.0%, and mood changes in 69.4% of cases. Among cases with hypothyroidism, 15.3% had diabetes, 2.4% type I and 12.9% type II. The association between hypothyroidism and diabetes was significant (P=0.003). There was also a significant association between hypothyroidism and age, sex, family history of hypothyroidism, obesity, and the presence of autoimmune diseases (P<0.05). As regards treatment, 61.9% of hypothyroidism cases took medical treatment, and only 49.4% improved.