Designing a pcb with transformer

I am looking for some pointers on developing a pcb with an AC main line transformer incorporated in the design. I have always just used an AC adapter before, but with this application I need to have the transformer on the board.

What I am worried about is the noise that may be brought into the system from adding the transformer. Any pointers or links to a good tutorial would be very helpful. Thanks.

I would imagine there's very little problem, but it depends really what the application is?, which you don't mention.