Evaluation was made of the effect of precommercial thinning in 13–15 year old Norway spruce (Picea abies (L.) Karst.),on the incidence ofHeterobasidion annosumin residual trees, more than 20 years after thinning. Five sites in southern Sweden were studied with the following treatments at each site: unthinned plot and plots thinned to 600, 1 000, 1 400, 1 800 and 2 500 stems ha−1. Only three trees out of 450 investigated, were found to be decayed. None of these trees were found to be infected byH. annosumas an effect of precommercial thinning. Control measures to prevent decay caused byH. annosumin residual trees do not appear warranted for precommercial thinning of young, planted, Norway spruce stands.