The deposition of titanium on a titanium alloy substrate is being examined for potential use as a surface treatment for medical prostheses. A Ti6Al4V alloy was coated with pure titanium by cold gas dynamic spraying (CGDS). Coatings were deposited onto samples with two different surface preparation methods (as-received and grit blasted). The fatigue life of the as-received and grit blasted materials, both before and following coating, was measured with a rotating-bend fatigue rig. An 18% reduction in fatigue life was observed following the application of the coating to the as-received substrate, but no significant reduction was observed on its application to the grit blasted substrate. The reduction in fatigue life has been related to the substrate-coating interface properties and residual stress states.