Reduced protein diets may be limiting in dietary nitrogen (N). The objective of this study was to determine the impact of non-protein nitrogen (NPN) inclusion and lysine content on growth performance of growing pigs. Pen-housed growing pigs were randomly assigned to one of six dietary treatments to test the impact of NPN inclusion and dietary lysine content for 28 days. NPN inclusion increased feed efficiency and lean depth (P < 0.05). Final body weight increased with greater lysine (P < 0.05) but was not impacted by NPN (P > 0.05). Ammonium phosphate may be an appropriate N source in N-limiting diets for pigs.