Spontaneous recurrent hemarthrosis after knee arthroplasty is reported to occur in 0.3%–1% of patients, likely secondary to hypertrophic vascular synovium. Five patients who underwent previous arthroplasty presented with spontaneous hemarthrosis. Selective arterial embolization was performed with spherical embolic particles (diameter range, 100–700 μm). Angiography demonstrated synovial hypervascularity with geniculate artery “tumor blush” appearance in all patients. Average time to resolution of effusion was 2.6 weeks, with no recurrences reported during follow-up (mean, 25.4 mo; range, 16–48 mo). Two patients experienced transient cutaneous ischemia. Selective geniculate artery embolization with spherical embolic particles is an effective treatment for spontaneous recurrent hemarthrosis of theknee.