We flew aerial line transect surveys between March 30 and May 3, 2012, to estimate the abundance of lesser prairie-chickens (Tympanuchus pallidicinctus) and lesser prairie-chicken leks in four habitat regions in the Great Plains U.S. Estimates were supplemented with data from surveys conducted by Texas Tech University in two regions in the Texas Panhandle and surveys conducted by the Oklahoma Department of Wildlife Conservation in Oklahoma. We also estimated the number of mixed species leks which contained both lesser and greater prairie-chickens (Tympanuchus cupido) and the number of hybrid lesser-greater prairie-chickens. The study area for 2012 included four regions containing the 2011 estimated occupied lesser prairie-chicken range: 1) Shinnery Oak Prairie Region located in eastern New Mexico-southwest Texas panhandle, 2) Sand Sagebrush Prairie Region located in southeastern Colorado-southwestern Kansas and western Oklahoma Panhandle, 3) Mixed Grass Prairie Region located in the northeast Texas panhandle-northwest Oklahoma-south central Kansas area, and 4) Short Grass/CRP Mosaic located in northwestern Kansas and eastern Colorado. We created a sampling frame over the study area consisting of 536 blocks – each 15 km by 15 km. We flew 512 transects within a probabilistic sample of 256 blocks totaling 7,680 km. We observed 36 lesser prairie-chicken leks, 26 greater prairie-chicken leks, 5 lesser and greater prairie-chicken mixed leks and 85 prairie-chicken groups not confirmed to be lekking for a total of 152 prairie-chicken groups. Texas Tech University and the Oklahoma Department of Wildlife Conservation flew transects in an additional 27 subjectively selected blocks and detected 10 lesser prairie-chicken leks and 7 groups not confirmed to be lekking. Combining these data we estimated a total of 3,174 lesser prairie-chicken leks (90% CI: 1,672 – 4,705) and 441 lesser and greater prairie-chicken mixed leks (90% CI: 92 - 967) in the study area. We estimated a total of 37,170 individual lesser prairie-chickens (90% CI: 23,632 – 50,704) and 309 hybrid lesser-greater prairie-chickens (90% CI: 191 - 456) in the study area.