Nuclear magnetic resonance (NMR) is a powerful tool to study the local structure of ultrathin magnetic films and multilayers. This is demonstrated with an NMR study of ultrathin molecular beam epitaxy-grown Co layers on single-crystal Cu( Ill), Cu( 110) and Pd( Ill) substrates. Co on Cu( Ill) results in a mixture of fcc and hcp phases and the Cu ( 111)/Co interface is near to per fect. Co on Cu(I 10) grows mainly fcc in long stripe-shaped islands with rotigh Co/Cu interfaces. Finally, Co on Pd( 111) gives a (111)-oriented fcc structure. The top surface is flat, but the Pd( 111)/Co surface is intermixed.