This study investigates whether the presence of serum and plasma anti-myelin oligodendrocyte glycoprotein (MOG) and anti-myelin basic protein (MBP) in patients presenting with a clinically isolated syndrome compatible with demyelination (CIS) predicts early conversion to multiple sclerosis (MS). Forty-seven patients with CIS (46 with optic neuritis) had anti-MOG and anti-MBP antibodies analysed at baseline, and clinical and magnetic resonance imaging assessments. There was no evidence that the MS status based on either the McDonald or Poser criteria relates to the antibody status.