Background: Renal infarction is an extremely rare disease. Although more than 95% of cases are symptomatic, there have been no previously reported asymptomatic cases, without any abnormal blood and urine test findings. Furthermore, the efficacy of long-term treatment of idiopathic renal infarction remains unknown.Case Presentation:A 63-year-old Japanese male underwent laparoscopy; a very low anterior resection of the rectum for lower rectal cancer (stage II) four years and five months prior to diagnosis with renal infarction. During the follow-up imaging studies, asymptomatic idiopathic renal infarction was found incidentally. The blood and urine test findings were normal. Contrast-enhanced computed tomography revealed a linearly bordered area of poor contrast in the dorsal region of the right kidney; however, no renal artery lesions, thromboembolic disease, or coagulation abnormalities were observed. Initial treatment with rivaroxaban 15 mg/day resulted in the remission of the infarcted lesion. The anticoagulation therapy was terminated after about 18 months without any incidences of re-infarction or bleeding events.Conclusions:We reported a very rare case of asymptomatic idiopathic renal infarction where blood and urine tests revealed no abnormal findings, and it was diagnosed incidentally during a post-treatment follow-up examination for lower rectal cancer. Long-term anticoagulant therapy for idiopathic renal infarction should be terminated at an appropriate time, taking the risk of bleeding into account.