I've just got multiple render windows working( in an MFC app ) by creating a swap chain for each one, then in the OnDraw function of each window, setting the render target to the back buffer associated with the swap chain, then doing the usual Clear, BeginScene, EndScene, Present cycle..... My problem is that if I create each swap chain with a back buffer size of more than 500 * 500 pixels, the contents of the buffer when displayed is just seemingly random video memory. Creating each swap chain with a back buffer size of less than or equal to 500 * 500 pixels works fine !. Is there a limit to the size of backbuffers you can create for swap chains ? It doesn't say this anywhere in the documentation and I get no errors returned from IDirect3DSwapChain9::CreateAdditionalSwapChain even when my back buffers are larger than 500*500 pixels. Anyone have any ideas ? Thanks.