Pollen contamination is a severe problem in production breeding programs since it reduces the expected gain. In an attempt to solve this problem Skogforsk created an isolation experiment in the advanced Scots pine (Pinus sylvestris) seed orchard Västerhus in Västerbotten, Sweden. This experiment involves covering blocks of trees with a tent during the pollination period so that they only can mate with each other inside. To evaluate the effects of this tent treatment one tree from inside a tent with supplementary mass pollination (SMP) and one tree from the open control were chosen for this study. 48 seeds from each tree were sampled and genotypes at 9 microsatellite (SSR) loci. The likelihood and exclusion methods for paternity assignment were used to establish the fathers to these seeds. The results showed 0% contamination inside the tent and 4-8% outside in the control. The number of fathers contributed to the fertilization of the 48 seeds was 9 inside and 15 outside. The selfing rate was unexpectedly high, 10% inside the tent and 19% outside. The mating system inside the tent need to be further evaluated to fully understand what other effect the treatment has on the future progeny.