The impact of precommercial thinning (PCT) on tree growth and stem quality in jack pine was examined. The study was based on a PCT trial established in 1966 in New Brunswick, Canada. Three thinning intensities, 1.22 m×1. 22 m (A), 1. 52 m×1.52 m (B), 2.13 m×2.13 m (C), and a control stand were studied and a total of 154 sample trees were collected from the trial. Mortality in jack pine stands decreased from 67.6% to 32.7% with increasing PCT intensity from A to C. With increasing thinning intensity, tree diameter, merchantable stem heights and volumes, stem taper, branch diameter, and total lumber volume recovery per tree increased. Yet, only the most intensive thinning intensity (C) showed a significant effect on total tree height and crown development. PCT increased clear stem length, yet had no significant effect on wood density.