It is important for cost, resource efficiency, and environmental reasons to improve nitrogen use efficiency (NUE), understood here to mean the change in grain yield per unit of N fertilizer applied relative to the control (i.e. zero N). Major research efforts are underway at genetic, physiology, and management levels in companies and public research institutions to achieve higher NUE.  However, because corn yield gains over time have been so dependent on increased plant density tolerance, there are concerns that yield gains at higher densities may be occurring at the expense of NUE. We will summarize the NUE results from recent Indiana studies involving various corn hybrids grown at multiple plant densities and N rates.  A potential artifact in these trials is that corn yields at zero N are often much lower at higher densities than at lower densities; therefore, some of the changes in apparent NUE may be skewed. The common methodology in these trials (involving grain and whole-plant N uptake measurements at maturity) will also permit the associated discussion of other N efficiency parameters (such as N internal efficiency, N recovery efficiency, and N harvest index).  These results have implications for future genetic and management research in NUE.