The Pristiphora ruficornis group, defined here based on the structure of the penis valve and the genetic data, includes morphologically and genetically highly similar species that remain taxonomically challenging. Study of most of the relevant type material, examination of female saws and male genitalia, some rearing experiments, and genetic data enabled us to solve most of the taxonomic problems involving northern European taxa. As a result, 17 species are recognised in northern Europe. The following synonymies are proposed: Pristiphora aterrima Lindqvist, 1977, syn. n. is synonymised with P. albitibia (Costa, 1859), P. brunniapex Lindqvist, 1960, syn. n. and P. coniceps Lindqvist, 1955, syn. n. both with P. subopaca Lindqvist, 1955, Nematus vitreipennis Eversmann in Kawall, 1864, syn. n. (nomen oblitum) with P. leucopus (Hellén, 1948) (nomen protectum), and Nematus (Pristiphora) ruficornis var. integer Hellén, 1948, syn. n. with P. ruficornis (Olivier, 1811). Lectotypes are designated for the following taxa: Nematus appendiculatus Hartig, 1837, Nematus cathoraticus Förster, 1854, Nematus (Pristiphora) bifidus Hellén, 1948, Nematus frigidus Boheman, 1865, Pristiphora adelungi Konow, 1902, Nematus vitreipennis Eversmann in Kawall, 1864, Nematus melanocarpus Hartig, 1840, Nematus wuestneii Stein, 1885, Pristiphora pusilla Malaise, 1921, and Nematus fraxini Hartig, 1837. An illustrated electronic key made with Lucid and a traditional dichotomous key are provided to facilitate identification of the species. In addition we report the first occurrence of distinctly asymmetrical penis valves in Pristiphora (in P. pusilla), a condition rarely observed in Hymenoptera.