BACKGROUND AND OBJECTIVE: Patients with small (<5 mm) unruptured intracranial aneurysms (UIAs) are at risk of subarachnoid hemorrhage, but risk assessment of these patients remains controversial in daily clinical practice. We aimed to identify the risk factors of aneurysmal rupture in these patients. METHODS: We retrospectively analyzed consecutive patients with small UIAs who were admitted to our center between February 2009 and December 2014. The enrolled patients were divided into ruptured and unruptured groups. The risk factors for aneurysmal rupture were determined using multivariate logistic regression analysis. RESULTS: A total of 548 patients with 618 small intracranial aneurysms (267 ruptured and 351 unruptured) were included. Univariate analysis showed that rupture of small aneurysms was related to sex, age, smoking, hypertension, aspect ratio, size ratio, irregular shape, aneurysm width, height, and neck diameter, and location at bifurcation or posterior circulation. Multivariate logistic regression showed that rupture was associated with bifurcation location (odds ratio [OR], 5.409; 95% confidence interval [CI], 3.656-8.001; P < 0.001), size ratio (OR, 3.092; 95% CI, 2.002-4.774; P < 0.001), location (OR, 2.624; 95% CI, 1.428-4.824; P = 0.002), hypertension (OR, 1.698; 95% CI, 1.1140-2.527; P = 0.009), and age at diagnosis of UIA (OR, 1.826; 95% CI, 1.225-2.723; P [0.003). CONCLUSIONS: This study showed that 70.4% of small ruptured intracranial aneurysms (< 5 mm) were located at parent artery bifurcations and that bifurcation location was a significant independent factor for the risk of rupture of small UIAs (< 5 mm). Prophylactic treatment should be recommended for small UIAs in this location.