With increasing emphasis in the meat sector on better and more consistent quality, carcass leanness and conformation is now an important issue for sheep breeders. In 1999, only 47% of all carcasses in the UK met the target specifications for weight, fat and conformation (MLC, 2000), highlighting the potential for improvement. In the current stratified crossbreeding system, crossbred wether lambs are a by-product of the production of dam line ewes for the lowland sector. If their carcass quality is sufficient, they can give a valuable boost to the economics of the breeding programme. Genetic improvement of carcass quality in crossing sire breeds would benefit the crossbred wethers, as well as filter through to the terminal sire cross lambs produced by the crossbred ewes. This work aims to assess the influence of selection index and live conformation score of crossing sires (in this case Bluefaced Leicesters) on growth and carcass quality traits of their crossbred progeny, as a first step towards designing a genetic improvement programme for crossing sire sheep.