Introduction: Patient co-morbidities contribute to survivability from out-of-hospital sudden cardiac arrest. Many studies have been conducted regarding contributing factors to sudden cardiac arrest survival, though very few studies have been published detailing specific analysis of morbid obesity association with return of spontaneous circulation (ROSC) in adults treated by paramedics. Methods: Adults in sudden cardiac arrest with resuscitation initiated, including at least one defibrillation, between July 1, 2016 and December 1, 2016 were enrolled. Due to an increasing prevalence of morbid obesity in the United States adult population, a novel defibrillation strategy, involving weight-based joule settings and double sequential external defibrillation (DSED) was initiated in June 2016. As exact body weight is logistically difficult to obtain in the EMS care environment, a paramedic-estimated weight at the time of resuscitation to be 100 kg or greater was deemed representative of “morbid obesity” for this analysis. All resuscitations were reviewed from electronic medical records (EMRs) completed by treating paramedics, alongside telemetry and defibrillation events recorded, transmitted, and analyzed in proprietary software (CODE-STAT, Physio-Control Corporation, Redmond, WA). ROSC was determined from both paramedic and hospital clinician EMRs reviewed by a paramedic researcher. Results: During the 5 month study period, paramedics involved treated 133 adults in sudden cardiac arrest involving perceived ventricular fibrillation that was treated with at least one defibrillation. 49/90 (54.4%) with weight <100 kg as estimated by paramedics at the time of resuscitative care achieved at least transient ROSC. Only 17/43 (39.5%) with estimated weight ≥100 kg achieved any ROSC, despite paramedics authorized to perform defibrillations at higher joule energy settings for such weight. The OR for ROSC if <100 kg estimated weight is 1.83 (95% CI 0.87-3.83), though given limited sample size p=0.11. Conclusion: While survival from out-of-hospital sudden cardiac arrest in adults is multi-factorial, the presence of morbid obesity, defined as estimated weight ≥100 kg, trends towards less ROSC. Continued community health efforts to decrease the prevalence of morbid obesity in the adult population may confer improved ability to survive out-of-hospital sudden cardiac arrest.