Atypical antipsychotics are now commonly used in the treatment of bipolar disorder, as they have been shown to have effects on mania as well as psychosis. Shortly after the introduction of atypical antipsychotics, several cases of associated hypomania and mania were reported. Ziprasidone is an atypical antipsychotic recently approved by the Food and Drug Administration for the treatment of psychosis. Although ziprasidone has also been shown to be effective in treating mania, it may be associated with the induction of mania or hypomania. We report four cases of mania associated with initiation of ziprasidone, which, to our knowledge, are the first reported for this drug in bipolar patients. As ziprasidone has substantial serotonergic and noradrenergic action, we hypothesize, it may more likely induce mania than other atypical antipsychotics. We advocate future studies to evaluate ziprasidone's efficacy in treating bipolar disorder and caution clinicians that induction of mania or hypomania may be possible with this agent.