['Our goal was to analyze the association of the level of antiphospholipid antibodies (aPLs) with stroke severity and outcome in patients with antiphospholipid syndrome (APS).', 'Observational study included consecutive patients with ischemic stroke younger than 55 years (2007-2012). We analyzed serum levels of aPLs, including anticardiolipin (aCL) antibodies, anti-β2-glycoprotein I antibodies (anti-β2GPI) and antiprothrombin antibodies (aPS/PT) within the first 48\u2009h after admission, and again, in the case of a positive result, at least 12 weeks after the first measurement. Stroke severity was measured by the National Institutes of Health Stroke Scale (NIHSS), and the three-month stroke outcome by the modified Rankin Scale (mRS). Multiple linear regression models were used to analyze the correlation between the aPLs and stroke severity and outcome.', 'Overall 255 stroke patients were included, 22 (8.6%) with APS. Among them, a positive correlation was found between immunoglobulin M (IgM) aCL levels within 48\u2009h and NIHSS (rho\u2009=\u20090.471; p\u2009=\u20090.027), as well as a tendency toward a positive correlation between immunoglobulin G (IgG) anti-β2GPI levels within 48\u2009h and three-month mRS (rho\u2009=\u20090.364; p\u2009=\u20090.096). Multiple linear regression analyses showed a positive correlation between levels of IgM aCL\u2009<\u200948\u2009h and the NIHSS (β-coefficient [standard error; SE]\u2009=\u20090.127 [0.044]), as well as the levels of IgG anti-β2GPIwithin 48\u2009h and the three-month mRS (β-coefficient [SE]\u2009=\u20090.034 [0.011]).'] Do antiphospholipid antibodies correlate with stroke severity and outcome in patients with antiphospholipid syndrome?