<b><i>Introduction:</i></b> The triglyceride glucose index (TyG index) is a simple and reliable surrogate marker of insulin resistance (IR) that can predict functional outcomes and mortality after acute ischemic stroke (AIS). However, it is unclear whether the TyG index is associated with functional outcomes in patients with stroke who receive reperfusion therapy. Thus, we aimed to explore the prognostic value of the TyG index for the clinical outcomes of patients with AIS who underwent reperfusion therapy. <b><i>Methods:</i></b> We retrospectively assessed patients with AIS, with occlusion of either the middle cerebral artery or internal carotid artery, who were evaluated using multiphase computed tomography angiography (mCTA) and received reperfusion therapy. The TyG index was calculated as “ln [fasting glucose level (mg/dL) × triglyceride level (mg/dL)]/2.” Collateral status was evaluated using mCTA based on the University of Calgary Scale. Clinical outcomes included 3-month functional outcomes, early neurological deterioration, recanalization status, and hemorrhagic transformation. <b><i>Results:</i></b> In all, 183 subjects (age 69.5 ± 12.4 years; men, 59.0%) were enrolled. The median initial National Institutes of Health Stroke Scale score was 15.0 (interquartile range [IQR] 11–18). The median TyG index was 4.8 (IQR, 4.6–5.1), and 158 patients had TyG levels &#x3e;4.49, which represents the presence of IR. On univariate analysis, a higher TyG index was associated with both early neurological deterioration (18.4 vs. 0.0%, <i>p</i> = 0.041) and a 3-month poor functional outcome (mRS3-6) (61.4 vs. 32.0%, <i>p</i> = 0.011). After adjusting for multiple variables, including age, sex, type of reperfusion therapy, recanalization status, initial stroke severity, type of stroke, and history of hypertension and diabetes, high TyG index remained an independent predictor of a poor 3-month functional outcome (adjusted OR, 5.22; <i>p</i> = 0.014). However, TyG levels were not significantly associated with collateral status (<i>p</i> = 0.756). <b><i>Conclusions:</i></b> IR, represented by a high TyG index, may predict poor 3-month functional outcomes in patients with AIS who undergo reperfusion therapy.