Using a completely randomized design, 72 individually penned pigs, comprising two genotypes (Masterbreeders Mastergilt × Large White and Sovereign × Large white progeny) with equal numbers of boars and gilts, were given food ad libitum from 25 to 60 kg live weight. From 60 to 120 kg one-third of the pigs continued to be given food ad libitum whilst the remainder were given one of two levels of restriction (0.85 and 0.925 of maintenance energy × 3.5). Diets were calculated to provide 13.8 and 13.0 MJ digestible energy (DE) per kg air-dry weight for growing and finishing phases respectively. Ultrasonic measurements of backfat at the P2 site were made at 10 kg intervals from 60 to 120 kg live weight and carcass measurements taken at slaughter. Complete dissection of ham joints was carried out. Predicted ad libitum intakes were based on established equations but daily intakes were much lower than these values and no treatment provided food restriction compared with them. Daily DE intakes (mean of both genotypes) obtained at 25, 60, 90 and 120 kg live weight were 204, 30.7, 36.2, and 414 MJ (i.e. 3.5, 3.1, 2.9 and 2.7 × maintenance). During the growing (25 to 60 kg live weight) and finishing (60 to 120 kg live weight) periods boars grew faster (P < 0.01 and P < 0.001) than gilts (881 v. 827 and 944 v. 806 g/day) with corresponding improvements in food conversion ratio (P < 0.001). Boars had lower killing-out proportions (0.787 v. 0.801; P < 0.001). Mean P2 values for boars and gilts were 13.2 and 13.9 mm respectively (excluding skin). Greater quantities of muscle were found in the hams of boars than gilts (662.7 v. 642.3 kg; P < 0.05) but no difference between the sexes for ‘eye muscle’ area was observed (43.3 v. 45.0 cm2). Results show the apparent potential of modern hybrids to achieve good growth rates despite moderate food intakes and their ability, even when given continuous access to food, to produce very lean carcasses at relatively heavy slaughter weights.