British hill sheep play several pivotal roles in the organization of sheep farming in the UK. They are required to give birth to and rear their lambs under harsh extensive conditions. This study investigate whether genetic selection for increased (LEAN) or decreased (FAT) carcass lean content in the Scottish Blackface breed over a 7 years had affected the ability of ewes to rear lambs by altering the expression of maternal and neonatal lamb behaviours. The behaviour of 61 ewes (32 LEAN and 29 FAT) and their 119 lambs were recorded at parturition and over the first 8 weeks of life. Overall there were very few effects of selection on the behaviour of the ewes. LEAN ewes were significantly faster than FAT ewes to start grooming their lambs after birth and FAT ewes tended to withdraw more frequently from their lambs than LEAN ewes. LEAN lambs were significantly quicker than FAT lambs to perform all righting movements (latency to stand), were more likely both to suck, and to play within the first 2 h of birth. The higher rate of sucking in LEAN lambs persisted over the first 3 days after birth, when LEAN lambs were also significantly closer to their mothers than FAT lambs. Thereafter, there were no significant effects of ewe or lamb line on behaviours recorded up to 8 weeks after birth. Overall lamb mortality to 8 weeks was 19.3% and was not significantly affected by lamb line. The results of this study suggest that, although ewe maternal behaviour has not been significantly affected by selection for lean growth, the activity of the neonatal lambs has been affected.