It is now well established that finishing diets for beef cattle containing a high proportion of grass silage produce lower growth rates and a greater proportion of fat in the gain than high-concentrate diets offered at the same energy input. However, a major proportion of beef cattle in the British Isles are finished off grass and there is little information on the carcass composition of grass-finished cattle relative to those finished on high-concentrate diets. Two comparative slaughter experiments involving both steers and heifers have been carried out to compare grazed grass and concentrate diets in terms of performance and carcass composition at equal levels of performance.