<b><i>Introduction:</i></b> Radiological indicators in head computed tomography (CT) scan have emerged as tools to evaluate sarcopenia using the sectional area and thickness of the temporal muscle. They can be obtained by standardized measurements in preoperative image assessment of patients with brain aneurysms. We aimed to evaluate the association between functional outcomes after interventions for intracranial aneurysms (IAs) and temporal muscle thickness (TMT) and area (TMA), as surrogates of sarcopenia. <b><i>Methods:</i></b> This is a prospective observational cohort study in patients who underwent microsurgery or embolization for ruptured or unruptured IA between January 2018 and December 2019, with a 6-month follow-up. Preoperative CT scans were analyzed to measure TMT and TMA. The functional outcome was assessed by the modified Rankin Scale (mRS). The main outcome was the relationship between sarcopenia and the postoperative functional outcome. <b><i>Results:</i></b> A total of 361 patients were included, of whom 199 (55.1%) had ruptured and 162 (44.9%) had unruptured lesions. Larger TMA significantly predicted better functional outcomes at discharge. TMT was associated with functional outcomes at both discharge and 6 months, adjusted for rupture and hypertension. Maximizing the sum sensitivity-specificity, an optimal TMT cutoff of 6.25 mm can predict unfavorable outcomes. Maximizing the positive predictive value × negative predictive value of a product, the cutpoint was 3.55 mm. <b><i>Conclusions:</i></b> Sarcopenia, represented by TMT and TMA, is associated with poorer functional results at discharge and 6-month follow-up in IA surgery. TMT below 6.25 mm was associated with unfavorable functional outcomes. These easily obtainable measurements may improve the decision-making process for patients with IAs.