Introduction: The prevalence of the obesity is increasing day by day globally. One of the most important factors causing obesity is thyroid dysfunction. The present study was aimed to assess the association between the serum Thyroid stimulating hormone (TSH) levels and the body mass index (BMI). Material and methods: 80 subjects were recruited in the study in which 40 were male and 40 were female. The age, gender, body weight and height were noted and the body mass index (BMI) was calculated. The serum thyroid stimulating hormone (TSH) levels were measured using ECLA method. The serum TSH levels were compared with age and the body mass Index (BMI). Results: The subjects were divided into 4 groups based on the body mass index. In the present study 6.25% of subjects were under weight, 12.5% subjects were normal weight, 17.5% were overweight, and 62.5% were obese. The mean TSH of underweight, normal weight, over weight and the obese groups were 13.36 ± 5.52 µIU/ml, 15.16 ± 5.77 µIU/ml, 26.30 ± 21.4 µIU/ml, and 61.66 ± 27.50 µIU/ml respectively. There was a strong positive correlation between the serum TSH levels and the body mass index and negative correlation between the age and the serum TSH levels. Conclusion: Based on the results of the present study, a highly significant association was found between the serum TSH levels and the body mass index. The mean TSH levels were higher in the obese subjects and there was no association between the serum TSH levels with the age and gender.