The folowing may get you going.

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
Application.EnableEvents = False

Dim Rw, Col, X
Rw = Target.Row: Col = Target.Column
For X = 1 To Rw - 1
If Cells(X, 1) = Target Then
Cells(Rw, 1).Font.ColorIndex = 3
End If
Next

Application.EnableEvents = True
End Sub

Assuming that the data is all in column 1 (A), duplicated entries will be
coloured RED.

regards,

don
--

"Simon" wrote in message
...
Is it possible to have a column of numbers and as I enter
new numbers to the column the cell changes colour if the
number already appears in the column.

Column

100052
100053
100098
100032


New number entered

100056 - No colour change

100053 - Cell colour changed


Many Thanks

Simon