Objective To investigate the association between angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism and cerebral vasospasm (CVS) in patients with spontaneous subarachnoid hemorrhage (SAH).Methods A total of 166 patients with spontaneous SAH were divided into CVS group (72 cases) and control group (94 cases) depending on presence or absence of CVS. The serum ACE level of the patients was determined by ELISA, and the ACE gene I/D polymorphism was determined by polymerase chain reaction-restriction fragment length polymorphism.Results There was no significant change in serum ACE level within 13 days after SAH (all P>0.05). The baseline serum ACE level of the patients in the CVS group was higher than that in the control group (t=2.136,P=0.048). There were significant differences in genotype and allele distribution frequency of the ACE gene I/D site between the CVS group and the control group (χ²=7.086,P=0.029; χ²=6.080,P=0.014). A multivariate logistic regression analysis showed that carrying the D allele at the ACE gene I/D site was a risk factor for CVS in patients with spontaneous SAH (odds ratio[OR]=1.473, 95% confidence interval[CI]:1.068-2.610, P=0.021).Conclusions The ACE gene I/D polymorphism may be correlated with the development of CVS in patients with spontaneous SAH.