remove duplicate elements from a Generic list

Hello,
  I have function that should query a directory and return files that match a pattern. However, the list contain duplicate elements. How do I remove duplicate element from list<string>

e,g searchPattern = cap|cap.gz
file = f1.cap, f2.cap.gz
* The code below will add the files twice

Public Function GetFilesByExtension(ByVal dir As String, ByVal searchPattern As String) As String()
    Dim filelist As New List(Of String)
    Dim m_arExt() As String = Split(searchPattern, "|")
     For Each FileExt As String In m_arExt
            filelist.AddRange((IO.Directory.GetFiles(dir, FileExt)))
        Next
return Return filelist.ToArray