Abstract Background Owing to inconsistent diagnostic criteria and small heterogeneous cohorts, little is known about the long-term outcomes of adult left ventricular noncompaction (LVNC), a rare cardiomyopathy with potentially serious outcomes. This systematic overview aimed to better delineate the natural history of adult LVNC. Method and Results A comprehensive computerized search using “noncompaction” and its synonyms initially identified 206 articles, with reference lists subsequently hand scanned. These searches yielded 5 studies that were eligible for this systematic overview, identifying adult cohorts with isolated LVNC diagnosed by similar echocardiographic criteria. This combined cohort (n = 241) was followed for a mean duration of 39 months. The annualized event rate was 4% for cardiovascular deaths, 6.2% for cardiovascular death and its surrogates (heart transplantation and appropriate implantable cardioverter-defibrillator shocks), and 8.6% for all cardiovascular events (death, stroke, implantable cardioverter-defibrillator shocks, and heart transplantation.) Familial occurrence of LVNC in first-degree relatives was identified by echocardiography in 30% of index cases who were screened. Conclusion LVNC is an increasingly recognized cardiomyopathy diagnosed by echocardiography and is associated with familial tendencies, arrhythmias, thromboembolism, advanced heart failure, and death.