Atrial fibrillation is a major health problem with risk of systemic arterial embolism. Acute embolic renal infarction is a rare condition with symptoms that are often nonspecific. We present a 36-year-old previously healthy man with acute embolic renal infarction secondary to new onset atrial fibrillation, who presented with flank pain mimicking renal colic. The patient was treated successfully with anticoagulation therapy, beta-blockers, broad-spectrum antibiotics, and supportive treatment.