If you are dealing with numbers, it is a cell  formatting issue.
Excel treats numbers in parens as negatives. if you change to the
accounting category, remove the dollar sign, you will return to a
number in parens.

For this to have happened, the contents  are numeric.
If you're wanting the "()" to show, you have two choices.
change the formatting of the cells to use () for negative  numbers:
"0.00_);(0.00)"
or change it to a text string.
which will cause you problems if you're trying to use add  the numbers.
If you're wanting to change the contents to text (to essentially
remove them from the calculations) use:

ActiveCell.Offset(1, 0).Value = "'(" & ActiveCell.Offset(1, 0).Value
& ")"
(note added single quote)

this got me closer. Unfortunately I lose the decimal
precision of the original value. For example, say the value in the
cell officially was 3.1412563, but I had the cell  rounded to 3.1.
After running the macro  with a tweak one way or the other I end up
with (3) or (3.1412563).

It's like I need to capture not the specific value of the cell, but
the displayed value.

Back to my original question.
Are you wanting to retain the numeric value?
or are you content with converting it to text?

Also, are all the values being displayed at the same
precision? (decimals to 1,2 or 3 places) or are they different?

I guess what I'm getting at is if you're wanting all of the values
displayed as,
say 2 place  decimals, you can use something like:

Cells(i, 5) = "'(" & Format(Cells(i, 1), "##,##0.00") & ")"

the result will be a text string.
If you're wanting the value to be forced to round down (or up, or truncate)
you'll have to do that to the cells(i,1) within the formula.

does this help?

Once we thought to use a round function we got it done. Thanks for
the help. I'm posting the entire script below in case anyone else
comes along trying to do this.

Selecting the top left corner of a table, it goes through and
compares each cell  to the one below it, deleting the matches and
placing the differences into parentheses rounded to one decimal
point.

Sub DataCompareDecimal()
Dim x As Integer

Do While ActiveCell.Value <> ""

Do While ActiveCell.Value <> ""
x = x + 1
If ActiveCell.Offset(1, 0) = ActiveCell.Value Then

ActiveCell.Offset(1, 0).Value = ""
ActiveCell.Offset(0, 1).Activate


Else
ActiveCell.Offset(1, 0).Value = "'" & "(" & Round
(ActiveCell.Offset(1, 0).Value, 1) & ")"
ActiveCell.Offset(0, 1).Activate

End If

Loop

ActiveCell.Offset(2, -x).Activate
x = 0

Loop

End Sub