Functions & equations don't, by themselves, perform actions (such as delete).
They return results. The steps I'd take:
On sheet 1, in cell E2 enter the formula
=if(isna(match(d2,Sheet2!D:D,false)),"","delete!") .
Copy that down (using autofill) to each row on sheet1.
Turn on autofilter (click one cell in the table then Data Filter
Autofilter)
Use the drop-down in E1 to select 'delete'.
Click in the first cell in column containing the word 'delete' and
ctrl+shift+down arrow to select all such cells.
Right-click and select DeleteRow.
--Bruce

"Luke Rogers" wrote:

The situation: I have two worksheets both of which have columns named:

1) Name
2: Address
3) Post Code
4) Telephone Number

I am using the telephone number as the unique identifier as we only have to
store data 'per household' - not 'per customer'.

On the first worksheet there is a list of all the customers.
On the second worksheet there is a list of customers who wish to be taken
off our customer list.

I need to use the second worksheet to delete the customer entries in the
first worksheet.

I have tried to use the worksheets together to identify duplicates but there
seems to be a problem doing this between two worksheets.

Can anyone tell me a simp way of putting this equation into excel:

if sheet2 single telephone number = any sheet 1 telephone number
then delete customer record from sheet1.

Thanks guys!