The main alterations reported in the thyroid profile of patients with obesity show an increase in TSH and T3 levels and a decrease in T4 levels. These alterations have been reported in 25% of obese patients and are considered more as a consequence rather than stemming from obesity itself. However, these alterations have not been evidenced in the Mex¬ican population. Objective: The objective of the study was to determine the association between TSH, T3, T4 levels, and obesity grade. Material and methods: This is a retrospective analytical cross-sectional study conducted between the years 2015 and 2019. Obese patients who had altered TSH, free T4 and total T3, and free T3 levels were included in the study. Patients diagnosed with diabetes, thyroid diseases, undergoing treatment with levothyroxine, or taking drugs that alter thyroid function tests were excluded. Spearman’s rank correlation coefficient was used to establish a correlation between obesity grade and thyroid hormones levels. Results: A positive correlation was found between TSH levels and obesity grade (r = 0.13; p = 0.049). A negative correlation was found between obesity grade and free T4 (r = −0.26; p = 0.000275) and total T4 levels (r = −0.18; p = 0.029). While analyzing free T3 and total T3 levels and T4/T3 ratio, the descriptive analysis showed an increase in T3 values as the obesity grade increased, with no correlation found. Conclusions: Obesity grade is associated with alterations in thyroid function that can affect the normal range of thyroid hormones levels.