Introduction: Pulmonary vein isolation (PVI) using radiofrequency (RF) and cryoballoon (Cryo) ablation are standard approaches for rhythm control of symptomatic atrial fibrillation. Both strategies involve scar formation of the left atrium (LA). There have been few studies investigating the differences in residual fibrosis and scar formation in patients undergoing RF and Cryo using cardiac magnetic resonance imaging (CMR).     Methods: The current study is a sub-analysis of the control arm of the Delayed-Enhancement MRI Determinant of Successful Catheter Ablation of Atrial Fibrillation study (DECAAF II). The study was a multicenter, randomized, controlled, single blinded trial that evaluated atrial arrhythmia recurrence (AAR) between PVI alone and PVI plus CMR atrial fibrosis guided ablation. Pre-ablation CMR and 3–6-month post ablation CMR were obtained to assess baseline LA fibrosis and scar formation respectively.     Results: Of the 843 patients randomized in the DECAAF II trial, we analyzed the 408 patients in the primary analysis control arm that received standard PVI. Five patients received combined RF and Cryo ablations so were excluded from this sub-analysis. Of the 403 patients analyzed, 345 underwent RF and 58 Cryo. The average procedure duration was 146 minutes for RF and 103 minutes for Cryo (p = 0.001). The rate of AAR at ~15 months occurred in 151 (43.8%) patients in the RF group and 28 (48.3%) patients in the Cryo group (p = 0.62). On 3-month post CMR the RF arm had significantly more covered fibrosis (3.6% vs. 3.0%, p = 0.04) and scar (8.8% vs. 6.4%, p = 0.001) compared to Cryo. Patients with ≥ 6.5% LA scar on 3-month post CMR had less AAR independent of ablation technique (RF p = 0.009, Cryo p = 0.02). Cryo caused a greater percentage of right and left pulmonary vein (PV) scar (p = 0.04, p = 0.02) and less non-PV scar (p = 0.009) compared to RF. On Cox regression Cryo patients free of AAR had a greater percentage of left PV scar (p = 0.01) and less non-PV scar (p = 0.004) compared to RF free of AAR.     Conclusion: In this sub-analysis of the control arm of the DECAAF II trial, there was no significant difference in the rate of AAR in patients undergoing PVI alone between RF vs. Cryo. Post ablation LA scar ≥ 6.5% predicted freedom from AAR, independent of ablation technique. Cryo formed a greater percentage of PV scar and less non-PV scar compared to RF, which may have prognostic implications.