John
Yes, it's possible. I'd suggest to select each range in turn and give them meaningful names and use those names e.g. in a SUM formula.
Suppose you want to total the numbers in A1:A5 on Sheet1 and the ones in C4: D5 on Sheet2. Select A1:A5 and name it (say RangeA) via the Name Box or the option Insert|Name|Define. Name C4:D5, say RangeB, following the same recept. The following will work:
=SUM(RangeA,RangeB)
Aladin
Yep, try =SUM(Sheet2!A1,Sheet3!A1,Sheet4!A1)
Or =SUM(Sheet2!A:A,Sheet3!A:A,Sheet4!A:A)
And if you're summing up the same cell (e.g., A5) from multiple worksheets (e.g., in an Annual worksheet for worksheets named jan, feb, ... dec), you could use sum(jan:dec!A5)