Abstract Background Mitral-annulus-disjunction (MAD), often described in mitral-valve-prolapse (MVP) patients, remains incompletely defined and its clinical outcome consequences are unknown. Objectives To assess MAD prevalence, clinical and echocardiographic characteristics, and independent impact on outcome in patients with isolated-MVP. Methods A cohort of 595 (65±16 years, 278 female) consecutive patients with MVP and comprehensive clinical, rhythmic and Doppler-echocardiographic characterization, was identified. Primary-endpoint was overall-survival, or occurrence of ventricular-arrhythmia. To eliminate clinical differences, we matched MAD-patients 1:1 with no-MAD based on propensity score for overall survival analysis using a greedy 5-to-1 digit-matching algorithm. Results MAD was frequent, present in 186 (31%) of MVP-patients and independently associated to bileaflet-MVP, leaflet-redundancy, younger-age, female-sex, enlarged left-ventricle-endsystolic-diameter and higher left-ventricle-ejection-fraction (all P≤0.04). Outcome primary-endpoint of survival after MVP diagnosis in matched-cohort (10-year 95±1%) was not associated with MAD presence (10-year 93±2% for no-MAD and 97±1% for MAD, P=0.4). Mortality was comparable for MAD (univariate-hazard-ratio 0.64 [0.25–1.65], P=0.4 vs. no-MAD), even adjusted-comprehensively including for MVP-characteristics (adjusted-hazard-ratio 1.17 [0.39–3.50], P=0.8). However, 220 (51%) MVP-patients were diagnosed ventricular-arrhythmia (161 with ventricular-tachycardia only) and long-term, MAD was associated with lower arrhythmia- and ventricular-tachycardia- overall freedom (adjusted-hazard-ratio for MAD 2.35 [1.75–3.15], P<0.0001 vs. no-MAD and 2.71 [1.93–3.82], P<0.0001 respectively). Hence, 10-year freedom of significant ventricular-arrhythmia in overall-cohort was severely reduced with MAD (41±4% vs. 62±3% for no-MAD). Conclusion In this unique MVP cohort, with arrhythmia and MAD comprehensively-characterized, MAD presence was frequent and independently associated to bileaflet-MVP and leaflet-redundancy. Long-term, MAD compared to no-MAD is not independently associated with higher-mortality but to reduced arrhythmia-freedom occurrence. Survival overall and by V arrhythmia Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Mayo Foundation