Objective:To investigate whether admission hyperglycemia predicts poststroke infections and, if so, whether poststroke infections modify the effect of admission hyperglycemia on functional outcome in ischemic stroke.Methods:We used data from acute ischemic stroke patients in the Preventive Antibiotics in Stroke Study (PASS), a multicenter randomized controlled trial (n = 2,550) investigating the effect of preventive antibiotics on functional outcome. Admission hyperglycemia was defined as blood glucose ≥7.8 mmol/L and poststroke infection as any infection during admission judged by an expert adjudication committee. Functional outcome at 3 months was assessed with the modified Rankin Scale.Results:Of 1,676 nondiabetic ischemic stroke patients, 338 (20%) had admission hyperglycemia. After adjustment for potential confounding variables, admission hyperglycemia was associated with poststroke infection (adjusted odds ratio [aOR] 2.31, 95% CI 1.31–4.07), worse 3-month functional outcome (common aOR 1.40, 95% CI 1.12–1.73), and 3-month mortality (aOR 2.11, 95% CI 1.40–3.19). Additional adjustment for poststroke infection in the functional outcome analysis, done to assess poststroke infection as an intermediate in the pathway from admission hyperglycemia to functional outcome, did not substantially change the model. In patients with recorded diabetes mellitus (n = 418), admission hyperglycemia was not associated with poststroke infection (aOR 0.49, 95% CI 0.15–1.58).Conclusions:In nondiabetic acute ischemic stroke patients, admission hyperglycemia is associated with poststroke infection and worse functional outcome. Poststroke infections did not modify the effect of admission hyperglycemia on functional outcome in ischemic stroke.