Objective : Chronic subdural hematoma[CSDH] is usually treated by burr hole trephination and hematoma evacuation with closed drainage and the surgical result is relatively good in most reported series. But, some patients experience the recurrence of CSDH. We study the clinical factors related to the recurrence of CSDH. Methods : 213 consecutive patients with CSDH who were treated with burr hole trephination and hematoma evacuation with closed drainage. The medical records, radiologic findings were reviewed retrospectively and clinical factors associated with the recurrent CSDH were analysed statistically. Results : 8.4%[18 cases] of the 213 patients who were treated due to CSDH were recurred. The demographic variables such as age, sex, coexisting diseases were not related to the recurrence. The preoperative hematoma thickness and postoperative hematoma thickness were not associated with the recurrence. The only factor related to the recurrence is postoperative hematoma density in this study. Conclusion : This study shows that postoperative hematoma density was strongly related to the recurrence of CSDH. However, several factors associated with the recurrent CSDH were reported in the liletrature. Thus, further study will be needed to uncover the factors related to the recurrence of CSDH.