Cerebrospinal fluid (CSF) diversion is an essential component of neurosurgical care, but the rates and significance of hemorrhage associated with external ventricular drainage (EVD) and ventriculoperitoneal (VP) shunt procedures have not been well quantified. In this retrospective study, the authors examined the frequencies of hemorrhagic complications associated with EVD and VP shunt procedures, and attempted to identify associated risk factors. The treatment records of 370 EVDs in 276 patients and 102 VP shunts in 96 patients performed between 2008 and 2010 were retrospectively reviewed. Post-insertion computed tomographic (CT) scans were analyzed for any new hemorrhage related to the ventricular catheter. The effects of diagnosis at admission, endovascular treatment, anti-platelet medication, and a concurrent craniotomy operation were included in the analysis conducted to identify risk factors of ventricular catheterrelated hemorrhage. Hemorrhage following EVD was detected on CT scans in 76 (20.5%) of the 370 cases. However, symptomatic hemorrhage occurred in only 5 cases (1.4% of all EVDs). VP shunt was associated with a higher incidence of ventricular catheter-related hemorrhage than EVD (hemorrhage rate: 43.1%) and the rate of detectable neurological change was 2.9%. Multivariate logistic-regression analysis of risk factors of EVD-related hemorrhage identified preoperative anti-platelet medication as the only significant factor (odds ratio, 3.583 [95% confidence interval, 1.353 to 9.486]; p = 0.010). Ventriculostomy-related hemorrhagic complications were more common than anticipated, especially for the VP shunt procedure. However, such hemorrhages are rarely large, rarely the cause of neurological deterioration, and rarely require surgical removal. Preoperative anti-platelet medication appears to affect EVD-related hemorrhage development.