During the prospective baseline period, the subject will maintain cyclical vomiting records in which all headache occurrences will be recorded and characterized. (Cyclical vomiting records will be maintained throughout the study). The purpose of this study is to assess the effectiveness, tolerability and safety of oral topiramate for the preventative management of Cyclic Vomiting Syndrome using a prospective design, established diagnostic criteria (ICHD 2004), and defined, objective primary and secondary endpoints.