The antiphospholipid (Hughes) syndrome (APS) includes systemic and central nervous system (CNS) pathology associated with antibodies to a complex of phospholipids and beta2-glycoprotein I (beta2-GPI). Beta2-GPI immunized mice develop systemic manifestations of APS and we presently examined CNS manifestations in this APS model. Female BALB/c mice were immunized once with beta2-GPI in complete Freund's adjuvant (CFA) or with CFA alone (controls). A staircase test and a T-maze alternation test were performed to test behavior and cognition in independent groups of mice 6, 12 and 18 weeks following the immunization. The APS mice developed elevated levels of antibodies against negatively charged phospholipids and beta2-GPI. Neurological impairment was detected only 18 weeks after the induction of the APS and consisted of both cognitive (53 +/- 4 vs 71 +/- 3% correct choices in the T-maze alternation for APS vs control mice, P < 0.001) and behavioral changes (higher number of rears (18 +/- 2 vs 11 +/- 1, P < 0.006) and higher number of stairs climbed (12 +/- 2 vs 7 +/- 1, P < 0.02). This is the first report of cognitive deficits in this APS model and demonstrates the time course for the development of previously described behavioral changes. The mechanism involved in these CNS manifestations remains to be elucidated.