Psocids are small insects that feed primarily on fungi, algae, lichens and organic detritus. Although they are relatively common in forest ecosystems, the general patterns in their abundance and diversity in boreal forests are still poorly known. We report records of 20 species of psocids quantitatively collected from four species of woody plants (Pinus sylvestris, Picea abies, Betula pubescens and B. pendula) at 50 sites in northern Europe, located between 59 degrees and 70 degrees N and between 10 degrees and 60 degrees E. Seven species were found only on conifers, seven other species only on birches and six species inhabited both birches and conifers. The overall density of psocids was 18.9 +/- 2.9 exx/kg (d.w. of plant material). Densities varied among the studied species of trees, being highest on P. abies and lowest on B. pendula. The species diversity was highest on B. pendula and lowest on B. pubescens. Both diversity and abundance of arboreal psocids in northern Europe decreased with latitude. However, due to the relatively low number of specimens collected, the conclusions about the diversity of psocids should be seen as tentative.