This paper consists of an unusual case history and an overview of the relationship between multiple sclerosis (MS), manic episode and corticosteroid treatment. Bipolar disorder and MS co-occur at a relatively higher rate. A 25-year old woman with a 7-year history of MS was admitted to our hospital with right side weakness. During the examination, she showed some manic behavior patterns and diagnosed as 'bipolar disorder-manic episode' by her psychiatrists. She was recommended for high dose steroids for her attack and antipsychotics for the manic episode but she refused the latter. Unexpectedly at the third day of steroid treatment, instead of being exacerbated, almost all of the manic symptoms disappeared. In the literature, this is the first report of a MS patient with bipolar disorder whose manic symptoms were cured after receiving steroids.