This paper examines the effects of delamination damage in composite to metal joints. Experiments on debonded double lap joints of graphite/epoxy to aluminium were conducted. Various debonded lengths were considered. Finite element analysis was also carried out in order to study the effect of debond length on various lap joints. The experimental and analytical results were found to be in good agreement. It is also shown that as the size of the damage is increased a stage is reached after which a significant further increase in damage does not result in a significant decrease in residual compressive strength.