Background: We evaluated the possible relationships between serum total homocysteine and folate and Vitamin B-12 in patients with intracranial aneurysm. Methods: We enrolled consecutive patients with intracranial aneurysm from the Han population who were admitted to the hospital, as well as control subjects who received medical examination on an outpatient basis. The serum total homocysteine, folate, and Vitamin B-12 levels were measured in patients with intracranial aneurysm and the control group, and the associations between those factors were analyzed using multivariate logistic analysis. Results: A total of 140 patients with intracranial aneurysm and 140 control subjects were enrolled from July 2014 to December 2015. The mean serum total homocysteine level in the patient group (19.98 +/- 10.84 mu mol/L) was significantly higher than that in the control group (15.13 +/- 5.55 mu mol/L, P < .001). The serum total homocysteine level was negatively correlated with folate and Vitamin B-12 levels (r = -.349, P < .001; r = -.531, P < .001, respectively) in the patient group. Homocysteine had an adjusted odds ratio of 2.196 (95% confidence interval: 1.188-4.057, P = .012) for the development of intracranial aneurysm. Conclusions: The present study provides evidence regarding the association between serum total homocysteine and folate and Vitamin B-12 in patients with intracranial aneurysm. Hyperhomocysteinemia is an independent risk factor for intracranial aneurysm, and folate and Vitamin B-12 are protective against intracranial aneurysm due to their roles in regulating the metabolism of homocysteine.