On the IRA Information Worksheet at Line 18 do I include the balance of an inherited IRA with my other IRAs?

No.    Inherited IRA's must be maintained and kept separate in the name of the deceased, with you as benificuary, and cannot be mixed with your own IRA's.

Unless is inherited from a spouse and you have chosen to treat it as your own IRA with the IRA custodian, then it becomes your IRA and is no longer inherited.

I am aware that these monies must be held separately.  The question is specifically about line 18 of the IRA Information Worksheet where the "combined value" of all traditional IRAs (including SEP and SIMPLE) is requested.  This implies the exclusion, rightfully so, of Roth accounts.  I would assume that the distinction is Roth vs non-Roth, i.e. post vs pre taxed accounts.  An inherited IRA can fall either way but given its somewhat unique circumstance I thought there may be some special handling required.