Grain sorghum is an important crop in the semi-arid regions. Productivity of grain sorghum is limited by soil fertility, especially nitrogen (N). Sorghum genotypes are known to vary in their response to nitrogen, however, the information on N use efficiency (NUE) is limited. Objectives of this research were to (a) determine the response of sorghum genotypes (hybrids and inbred lines) to N; and (b) quantify genotypic differences in nitrogen use efficiency. Field experiments were conducted at three locations (Hays, Ottawa and Manhattan, Kansas) in 2010. Six hybrids and six inbred lines were grown at three N regimes; 0, 45 and 90 kg N ha-1. Experimental design was a split-plot design with N as main plots and genotypes as sub-plots, with four replications. Planting was done in May and June across all the locations, and N fertilizer (Urea, 46%N) was applied at emergence. Data on biomass was measured at vegetative, flowering and maturity, and grain yield at maturity. Concentrations of N in the grain and components of NUE were determined for Ottawa. There were significant effects (P