['After acute ischemic stroke, the proportion of patients with detectable lesions on fluid-attenuated inversion recovery (FLAIR) MRI sequences increases over time. We investigated whether thrombolysis was less effective in FLAIR-positive versus -negative patients.', 'In this single-center hospital-based study, all consecutive patients with ischemic stroke who underwent an MRI before and 24 hours after thrombolysis between May 2008 and October 2009 were included. Patients were included if exact time of onset was known and thrombolysis was performed within 3 hours up until August 2008 and within 4.5 hours from September 2008 on. Blinded to time of symptom onset, 3 raters independently judged the visibility of lesions on FLAIR. Lesion volumes on diffusion-weighted imaging as well as National Institutes of Health Stroke Scale before and 1 day after thrombolysis were determined.', 'Of 51 patients (25 females, mean age 71, median National Institutes of Health Stroke Scale 6), 26 were FLAIR-positive. Neither lesion growth nor change in National Institutes of Health Stroke Scale differed significantly between FLAIR-positive versus -negative patients: median growth 2.6 mL (interquartile growth, -0.1 to 17.6) versus 0.8 mL (interquartile range, 0.1 to 17.8) and change in National Institutes of Health Stroke Scale -2.5 (interquartile range, -5 to 0) versus -2.0 (interquartile range, -5 to 0.5), respectively (P>0.5, Mann-Whitney rank sum test).'] Do clinical and radiological courses differ between fluid-attenuated inversion recovery-positive and negative patients with stroke after thrombolysis?