Antiphospholipid syndrome (APS) is an autoimmune disease which is characterized by thrombosis of different localization and antiphospholipid antibodies (aPL) production. The main neurological APS manifestation is ischemic stroke but sometimes APS can mimic multiple sclerosis. To compare clinical and laboratory features of APS-MS and MS, 16 patients with APS-MS and 30 age- and sex-matched patients with MS were studied. The clinical similarity of APS-MS and MS was determined by remittent neurological symptoms and the presence of multiple lesions in white hemisphere matter on MRI. The main distinguishing feature was the presence of typical clinical APS manifestations (thrombosis, miscarriage, thrombocytopenia, anemia, epilepsy, chorea, in the past history) in APS-MS patients while they occurred very rarely in MS (3%, p<0,05). All APS-MS patients had aPL (aCL - 75%, LA - 69%), in MS they were rarely found (aCL - 14%, low positivity; LA - 23%, weak activity). MS patients were more disabled and more often showed signs of spinal cord and brain stem damage than APS-MS patients while the latter oftener showed signs of sensory neuropathy. The MRT and visual evoked potentials study did not help to distinguish between APS-MS and MS. In conclusion, differential diagnosis between APS-MS and MS is based on the presence of typical clinical and immunological markers of APS in APS-MS patients and some peculiarities of local neurological symptoms. It is suggested that white matter damage in APS-MS is primary immunological mediated but not the result of brain ischemia. However the pathogenetically significant antibodies are not yet defined and should be elucidated.