Obstructive sleep apnea (OSA) is a disease of multicasual etiology. The risk factors include obesity, among other issues. Hence, it is extremely important to determine the effect of body weight on the severity of OSA. The aim of the study was to evaluate the influence of the body weight expressed as body mass index (BMI), on the value of upper airways diameter and on the AHI (Apnea-Hypopnea Index) value. The study was comprised of 41 patients diagnosed with OSA by way of polysomnography. Each patient was first examine via a lateral cephalometric image of the skull, which served to measure the upper and lower diameter of the upper airways. BMI was also calculated for each patient. Statistical analysis was carried out in accordance with Pearson’s correlation coefficient test. Our work demonstrated a negative correlation between BMI and the diameter of the upper airways, and a positive correlation between BMI and AHI value. We thus put forward that the increase in body weight in patients with OSA can contribute to the severity of the disease, regardless of the fact that it may not lead to a reduction of the lumen of the upper airways.