In 1941, the Canadian Forestry Service (CFS) established a commercial thinning trial in a 77-year-old lodgepole pine-dominated stand near Kananaskis, Alberta. Seventy percent of the total volume was removed, and density was reduced from 7 166 to 1 710 trees per hectare. Sample plots established in 1949 were remeasured in 1999; results are presented together with some earlier results. Thinning increased diameter growth and net periodic total volume increment. Twenty-two years after thinning (at age 99) the cumulative volume yield of lodgepole pine was 111 m3/ha, or 44%, greater than that of the control treatment. This yield increase rose to 66% by age 135, 58 years after thinning. Results suggest that dense, late-rotation lodgepole pine stands can respond to thinning with increased volume growth.