To determine the utility of TNF-α receptor (TNFR1) as a biomarker for the presence of aneurysms in patients with acute subarachnoid hemorrhage (SAH). This is a prospective study in patients with acute spontaneous SAH. Arterial blood from catheter near aneurysm and peripheral venous blood samples are collected. TNFR1 levels were analyzed in patients with and without aneurysm. 80 patients were included, 58 were analyzed. 41 patients (70.7%) had an aneurysm. Venous TNFR1 levels >1658 pg/ml had 46.3% sensitivity and 94.1% specificity for aneurysms presence. TNFR1 >1658 pg/ml was also an independent predictor for its presence (odds ratio = 12.03 [1.13–128.16]; p = 0.039). High levels of TNFR1 in peripheral venous blood are associated with the presence of aneurysm in patients with acute SAH. Subarachnoid hemorrhage (SAH) is a neurological emergency, in many cases caused by the rupture of a cerebral aneurysm. Usually aneurysms are detected in imaging tests, but sometimes they can be very small and go unnoticed. TNF-α is an inflammatory biomarker related to the presence and rupture of intracranial aneurysms and its receptor, TNFR1, could be detected in peripheral blood. This study demonstrates that elevated peripheral blood TNFR1 values are related to the presence of intracranial aneurysms in patients with acute subarachnoid hemorrhage. Following further research, it could become a useful tool for detecting small aneurysms in addition to conventional imaging tests.