Antibodies to beta(2)-glycoprotein (beta(2)-GPI) have been associated with recurrent thrombotic events in patients with systemic lupus erythematosus. The present study investigated the prevalence of antibodies to beta(2)-GPI in an unselected group of patients with ischemic stroke. One hundred and twenty-one sera from patients with ischemic stroke and 174 control sera from patients with nonischemic neurological disorders (n = 43) and healthy subjects (n = 131) were tested for antibodies to beta(2)-GPI by a solid-phase ELISA. Twenty-nine stroke patients (24%) had antibodies to beta(2)-GPI. Of the 43 patients in the neurological control group, 2 were positive. For comparison between the groups, Fisher's exact test was used for categorical variables and ANOVA for antibody titers. Antibody levels and frequencies of positivity were significantly different between the study groups. None of the sera from the healthy control group had abnormal antibody levels. When risk factors and associated diseases were taken into account, a marginal association was found between the presence of antibodies to beta(2)-GPI and hypertension (p = 0.036). This study demonstrates a significant prevalence of antibodies to beta(2)-GPI in an unselected stroke population.