Objective: To evaluate the relation between bother and overactive bladder (OAB) symptoms in patients with benign prostatic hyperplasia (BPH) patients using questionnaires: the BPH Impact Index (BII) and the OAB symptom score (OABSS). Annoyance from BPH usually provides the basis for a patient's decision to seek medical treatment. However, a study investigating the bother caused by OAB symptoms in patients with BPH and OAB has not been fully conducted. Methods: The present study included 100 male patients who were diagnosed with BPH and OAB according to questionnaire criteria. All patients were instructed to take tamsulosin for 28 days. The relation between the BII and OABSS was assessed to determine the factors influencing OAB symptoms on the BII before and after treatment. Results: The BII correlated positively with the OABSS, and multivariate analysis showed that the subscore of urgency was the only independent factor influencing the BII. Even after treatment, lower urinary tract symptoms were diagnosed as OAB using the OABSS criteria in 45 (45.0%) of the 100 patients. In these patients, the BII still correlated positively with the OABSS. However, multivariate analysis showed that the subscore of urgency incontinence, not urgency, was the only independent factor influencing the BII, although the subscore of urgency incontinence was significantly decreased with tamsulosin treatment. Conclusion: The degree of bother correlated with the degree of OAB symptoms in patients with BPH and OAB at baseline and after treatment with tamsulosin. The OAB symptom causing the bother was altered by treatment with tamsulosin in these patients.