New-onset atrial fibrillation (AF) occurring during acute medical illness or post-operatively has long been considered a benign phenomenon, and its recurrence risk was deemed low. However, recent data suggest a high risk of AF recurrence, and a thromboembolic risk similar to the risk associated with AF occurring without a provoking factor. As we lack interventional data, there are currently no guidelines on the long-term management of new-onset AF occurring during an acute medical condition. This paper aims to review current knowledge on epidemiology, recurrence risk, thromboembolic risk and anticoagulation strategies in the setting of new-onset AF occurring transiently with acute stress.