BACKGROUND: Out-of-hospital cardiac arrests (OHCA) are a major global health concern, occurring frequently worldwide. Obesity may impact outcomes in OHCA patients. OBJECTIVES: This study aimed to assess the impact of obesity on the return of spontaneous circulation (ROSC) in OHCA patients, considering sex differences. MATERIAL AND METHODS: A retrospective cohort study was conducted, analyzing medical records of patients assisted by the Emergency Medical System (EMS) in Poland from January 2021 to June 2022. The study included 33,636 patients with OHCA. Obesity status was determined using ICD-10 codes (E66) and descriptive diagnoses recorded by EMS teams. RESULTS: Univariate analysis indicated that obesity decreased the odds of ROSC by 25.47% (odds ratio (OR) = 0.75, 95% confidence interval (95% CI): 0.61-0.92) in women and by 19.76% (OR = 0.80, 95% CI: 0.66-0.97) in men. However, multivariate analysis, adjusting for confounding variables, did not confirm a statistically significant impact of obesity on ROSC outcomes. The likelihood of ROSC was significantly higher in individuals with an initial ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) rhythm compared to Asystole/pulseless electrical activity (PEA), being 4.204 times higher in women (95% CI: 3.525-5.014) and 3.655 times in men (95% CI: 3.320-4.023). Out-of-hospital cardiac arrest in a public place increased the odds of ROSC more than twofold for both sexes (women: OR = 2.20, 95% CI: 2.00-2.43; men: OR = 2.13, 95% CI: 1.98-2.29). Among women without obesity, hypertension decreased the odds of ROSC by 11.11% (OR = 0.89, 95% CI: 0.81-0.99). CONCLUSIONS: Our study demonstrated that obesity was not an independent predictor of ROSC in OHCA patients. Different predictors of ROSC were identified for men and women. Initial VF/pVT rhythm, location of OHCA and age were the significant factors influencing ROSC.