One hundred and eight Charolais cross steers were used to compare forage versus grain feeding as affected by slaughter endpoint on carcass composition and palatability attributes of beef. Diets included a 97% alfalfa silage ration or 68% high moisture corn, 25% alfalfa silage ration from start of test to finish or a ration of 97% alfalfa silage from start of test to day 42 of the trial followed by the 68% high moisture corn ration until slaughter. Cattle were slaughtered at either 4, 7, or 10 mm ultrasound backfat. Grain feeding increased (P = 0.01) average daily gain and decreased (P = 0.01) days to finish, while carcass weight and grade fat were similar (P > 0.10) between diets. Palatability attributes were generally unaffected by diet with the exception of slightly less (P = 0.09) beef flavour and more (P = 0.01) off flavour in forage-fed beef versus grain-fed beef. Higher (P = 0.01) concentrations of linolenic acid and lower (P = 0.09) concentrations of oleic acid in forage-fed beef may be partially responsible for diet differences in flavour. As slaughter endpoint increased from 4 to 7 mm backfat, average daily gain, days to finish, and carcass weight increased (P = 0.01). Palatability attributes assessing juiciness and flavour did not differ (P > 0.10) between slaughter endpoints. Beef from cattle slaughtered at 10 mm backfat was rated higher (P < 0.05) for softness, tenderness, and chewiness than beef from cattle slaughtered at 4 and 7 mm finish. Slaughter endpoint effects on "tenderness" attributes may partially explain why less tender beef is entering the marketplace. Key words: Beef cattle, alfalfa, grain, palatability, shear, fatty acids