The effect of stump treatment with three different agents (creosote, 10% aqueous solution of sodium nitrite and 20% aqueous solution of urea) on the spread rate of butt rot in Danish permanent forest yield research plots of pure Norway spruce(Picea abies(L.) Karst.) was evaluated. In total, 59 000 stumps from 622 thinnings were used in the calculations. Each thinning was regarded as one observation. To calculate the spread rate of butt rot, the butt rot incidence and possible stump treatment in previous thinnings were used as variables in the subsequent thinnings. If the previous thinning was carried out with urea as the stump treatment agent, the spread rate of butt rot (% year"1) was less than half that of the spread rate if the previous thinning had been carried out without stump treatment, and if the thinning prior to the previous thinning was carried out with urea, the spread rate was less than one‐third. Sodium nitrite also reduced the spread rate of butt rot but was not as effective as urea. Creosote had no effect on the spread rate. Plots on old hardwood forest sites showed a faster development of butt rot than either plots on old field sites or plots on old coniferous forest or old heathland sites.