We flew aerial line-transect surveys to estimate the range-wide population size of lesser prairie-chickens (Tympanuchus pallidicinctus) in the Great Plains, United States in 2012 and 2013. We also estimated the number of lesser prairie-chicken leks, the number of mixed-species leks that contained both lesser and greater prairie-chickens (T. cupido) and the number of hybrid lesser–greater prairie-chickens where these species' ranges overlap. The study area included the 2011 estimated occupied lesser prairie-chicken range in 5 states and was divided into 4 ecoregions. We created a sampling frame over the study area, consisting of 536 15- × 15-km grid cells. We flew 512 transects within a probabilistic sample of 256 cells totaling 7,680 km in 2012 and 566 transects within a probabilistic sample of 283 cells totaling 8,490 km in 2013. We estimated a total of 34,440 individual lesser prairie-chickens in 2012 (17,615 in 2013) and 350 hybrid lesser–greater prairie-chickens in 2012 (342 in 2013) in the study area. We estimated a total of 2,930 lesser prairie-chicken leks in 2012 (2,037 in 2013) and 453 lesser and greater prairie-chicken mixed leks in 2012 (356 in 2013) in the study area. We discuss the implications of alternative sampling designs with regard to conservation questions to be addressed. © 2014 The Wildlife Society.