The Goal: The aim of the study was to investigate whether stroke volume or the presence of ischemic stroke lesion on follow-up computed tomography 1 day after admission had association with sleep apnea among ischemic stroke patients undergoing thrombolysis. Materials and Methods: We prospectively recruited 110 consecutive ischemic stroke patients and performed computed tomography on admission and after 24 hours after intravenous thrombolysis. Stroke volume was measured from post-thrombolysis computed tomography scans. Unattended cardiorespiratory polygraphy with a 3-channel device was performed during 48 hours after admission. Findings: Of 110 ischemic stroke patients treated with thrombolysis 65.5% were men. Mean age was 65.8 years and body mass index 27.5 kg/m2. The mean Epworth sleepiness scale score was 4.7. Eight patients (12.7%) with visible acute stroke after thrombolysis and none in the other group had hemorrhage as complication (P ˂ .001). Sleep apnea, determined as a respiratory event index greater than or equal to 5/hour, was diagnosed in 96.4% patients. Respiratory event index greater than 15/h was found in 72.8% of patients. Both mean baseline oxygen desaturation index (23.9 versus 16.5, P = .028) and obstructive apneas/hour (6.2 versus 2.7, P = .007) were higher in visible stroke group. Stroke volume (mean 15.9 mL) correlated with proportion of time spent below saturation less than 90%, P = .025. Conclusions: Acute ischemic stroke patients treated with thrombolysis with visible stroke were more likely to have nocturnal hypoxemia than patients with not visible strokes. Stroke volume correlated with time spent below saturation of 90%.