How to sort dates correctly?

Hi, Excel-ers,

I think this should be pretty simple, but I can't figure it out...
Using Excel 2007, I made a column of Dates by:
=MONTH(D1)&"/"&DAY(D1)
and it looks like:
1/11
1/2
1/23
1/25
1/5
1/7
11/1
and the problem is... THAT's how they come out as Sorted !

How can I get them sorted correctly?

Thanks.

Mark53