Cerebral venous thrombosis (CVT) has been described in several cases of clinically definite multiple sclerosis (MS). In the majority of these, lumbar puncture followed by intravenous corticosteroid treatment was suspected as the cause. We report what is, to our knowledge, the first case of a patient with a multifocal clinically isolated syndrome suggestive of MS onset, who developed multiple CVT after lumbar puncture and during high-dose i.v. corticosteroid treatment We conclude that the sequence 'lumbar puncture followed by corticosteroid treatment' may be a contributory risk factor for the development of CVT when associated with other risk factors.