You can use a macro named Auto_Open() in a General module:

Option Explicit
Sub Auto_Open()
msgbox "hi"
End Sub

If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm

Peanut wrote:

Is there a way to create a macro that runs immediately upon opening of a
worksheet?

--

Dave Peterson