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In patients with acute stroke, previous research has also shown sex to affect outcome after intravenous thrombolysis (IVT) treatment; although outcome was similar between men and women treated with placebo, outcome was better in women after IVT. 4 The biological explanation for this difference remains unclear.A possible explanation could be the difference in recanalization. Women have more cardioembolic strokes, with uniform fibrin-rich clots and therefore a higher affinity of alteplase, resulting in more frequent, faster, and complete recanalization. [5][6][7] Another suggested mechanism could be a difference in endogenous fibrinolysis because of differences in sex hormones between men and women. Estrogen has an indirect influence on the controlling of the fibrinolytic system, as well as a direct neuroprotective activity. [8][9][10][11] However, there are no convincing data to support these hypotheses.Background and Purpose-Women have a worse outcome after stroke compared with men, although in intravenous thrombolysis (IVT)-treated patients, women seem to benefit more. Besides sex differences, age has also a possible effect on functional outcome. The interaction of sex on the functional outcome in IVT-treated patients in relation to age remains complex. The purpose of this study was to compare outcome after IVT between women and men with regard to age in a large multicenter European cohort reflecting daily clinical practice of acute stroke care. Methods-Data were obtained from IVT registries of 12 European tertiary hospitals. The primary outcome was poor functional outcome, defined as a modified Rankin scale score of 3 to 6 at 3 months. We stratified outcome by age in decades. Safety measures were symptomatic intracranial hemorrhage and mortality at 3 months. Results-In this cohort, 9495 patients were treated with IVT, and 4170 (43.9%) were women with a mean age of 71.9 years.After adjustments for baseline differences, female sex remained associated with poor functional outcome (odds ratio, 1.15; 95% confidence interval, 1.02-1.31). There was no association between sex and functional outcome when data were stratified by age. Symptomatic intracranial hemorrhage rate was similar in both sexes (adjusted odds ratio, 0.93; 95% confidence interval, 0.73-1.19), whereas mortality was lower among women (adjusted odds ratio, 0.83; 95% confidence interval, 0.70-0.99). Conclusions-In this large cohort of IVT-treated patients, women more often had poor functional outcome compared with men. This difference was not dependent on age. (Stroke. 2017;48:699-703.