Chronic subdural hematoma (CSDH) is a common neurosurgical condition and neurological condition improves after treatment in most patients. Recently more patients have poor prognosis because of aging of the population and presence of multiple comorbidities. The risk factors for poor prognosis, including postoperative delirium, were retrospectively evaluated to assess appropriate operative procedures. This study included 108 patients who underwent primary surgery from 2016 to 2017 at a single center. Operative procedures were drainage with or without irrigation. Functional outcome at discharge assessed the effect of various factors including postoperative delirium and operative procedure. Twenty-nine of 108 patients (27%) had worsened modified Rankin Scale (mRS) score at discharge, most with mobility disturbance or deteriorated cognitive function. Multivariate analysis found higher age (odds ratio OR = 5.13; 95% confidence interval CI = 1.0-1.14), poor pre-hospital mRS score (OR = 1.57; 95% CI = 1.0-2.46), and preoperative consciousness disturbance caused by CSDH (OR = 5.13; 95% CI = 1.27-20) were significant predictors of poor outcome. Operative procedure was not significantly related to functional outcome or recurrence, but irrigation was significantly related to postoperative delirium (OR = 4.83; 95% CI = 1.09-21.7). Patients with postoperative delirium were likely to require longer hospitalization stays (P = 0.028). Higher age, poor pre-hospital mRS, and preoperative consciousness disturbance caused by CSDH are the risk factors for poor recovery after CSDH. Irrigation is significantly likely to cause postoperative delirium and longer hospital stay.