Obesity epidemic is a major health-care problem. The thyroid hormone affects weight status through modulation of the Resting Energy Expenditure. This is done through the adaptive thermogenesis, the Na/K pump, glucose entry through GLUT-4 transporter, and through effects on the cardiac muscle. Studies conflict on the effect of obesity on the thyroid hormone function; some studies found a positive correlation even after excluding thyroid disorders, but others did not. Although obesity can explain the co-occurrence of coronary artery disease and diabetes mellitus, the influence of the thyroid hormone needs further clarification. In this study, we explore the association between obesity and thyroid hormone levels and the effect of the thyroid hormone on comorbidities. Methodology: This is a retrospective cross-sectional study that included hospitalized patients in the Endocrinology department of King Fahd Hospital between January 2016 and January 2017. Patient files were searched for age, gender, co-morbidities, chronic medications, TSH, free T3, free T4, and BMI. Patient with endocrinologic disease, thyroid disease, cancer; and women who are pregnant or on Oral Contraceptive Pills were excluded from the study. Data was analyzed using SPSS version 23. Frequencies, descriptive statistics and multiple linear regression were performed looking for statistically significant associations. Results: We studied 334 Saudi Arabian participants, 66.7% of whom were females. The mean age among our patients was 49 years. Twenty five percent of our patients had a normal BMI, 30.8% were overweight, and 42.8% were obese. Sixty three percent of our participants had abnormal TSH level, 22% had abnormal T3, and 21.5% had abnormal T4. About half of our patients had at least one comorbidity. Multiple linear regression analysis was done, with BMI as the outcome variable and TSH, T3, and T4 as the predictive variables. It did not reveal any significant association. Discussion: Although many studies report an association between obesity and the thyroid function, many others, including our study, did not. This can be attributed to different laboratories, methodologies and sample sizes. Our studied population was leaner on average than other studies. Although it is not clear whether different obesity levels have different effect on the thyroid function, an association was detected in more obese populations.