Our understanding of the critical shift in life history among insect parasitoids from ectoparasitism to endoparasitism is hindered by the fact that this particular life history trait is not known for many phylogenetically important taxa. One method of coping with this problem is to seek correlations between the ovipositor structure and this life history trait among taxa whose life history is known, and then to use this to infer the trait in species whose life history in unknown. In one group of parasitoid wasps, the Ichneumonoidea (Hymenoptera), we scored a total of 20 morphometric and morphological characters of the ovipositor for 41 species whose life histories are known – representing all the main clades in which there have been independent transitions to endoparasitism plus a broad range of the ectoparasitoid groups; we then used phylogenetic regression and discriminant analyses to infer the life history of four species whose life histories are unknown. To allow for the effect of phylogenetic non-independence in the discriminant analysis, we carried out analyses using different randomly chosen representatives of the endoparasitoid clades (phylogenetic regression controls for phylogeny). These two methods gave congruent results from which we conclude that Megalohelcon and Gnamptodon are endoparasitoids, and Aspilodemon and Allobracon are ectoparasitoids. We discuss the consequences of these inferences for our understanding of the evolution of endoparasitism in the Ichneumonoidea. © 2003 The Linnean Society of London. Zoological Journal of the Linnean Society, 2003, 139, 213–228.