During the year I957 a species of Saw flies new to Sweden, Gilpinia verticalis Guss., appeared in the province of Medelpad in North Sweden. The species had attacked Scotch Pine planted on an area of about 200 acres. After a discussion of the taxonomic position of G. verticalis in relation to genus Diprion Geoffr. (s. lat.), the author reports about the biology. He also gives an account of predators and hymenopterous parasites. Finally he is treating G. verticalis from an economical standpoint.