The aim of the study was to investigate how obesity can influence sleep respiratory parameters in obstructive sleep apnea syndrome (OSAS) in children. Methods: The study analyzes 56 Caucasian children and adolescents aged 11 ± 2.79 years with a BMI > 5th percentiles and a PSQ value ≥ 0.33. Children were divided into Obesity Group (OG) with BMI ≥ 95th and Control Group (CG) with 5th < BMI > 95th percentile. All selected children underwent PG. Respiratory parameters AHI (Apnea–Hypopnea Index), SaO2 (Saturation of Oxygen), ODI (Oxygen Desaturation Index), and Nadir (the lowest value of SaO2 registered during PG) were extracted from the PG. AHI was used to divide the severity of OSAS into four levels: snoring (AHI ≤ 1), mild (AHI > 1 and ≤5), moderate (AHI > 5 and <10), and severe (AHI ≥ 10). Results: The comparison analysis between the OG and CG showed a statistical significance only for ODI (p = 0.02). A statistically significant correlation between BMI and AHI (r = 0.02), SaO2 (r = 0.01), and Nadir O2 (r = 0.02) was found. Conclusions: There was no strong correlation between obesity and OSAS, but a positive association was found between BMI and AHI severity.