OAB occurs in approximately 50% to 75% of men with BPO and up to 38% of men with BPO continue to suffer from OAB after relief the obstruction.Symptoms of OAB are more bothersome than the voiding complaints of slow stream and hesitancy. However, the patients with both BPO and OAB are often not treated with muscarinic receptor antagonists due to concern that they will experience acute urinary retention.