Birth weight (BW) and gestation length (GL) have important implications for the survival and early vigour of the lamb, in turn affecting the early growth. In hill sheep BW and early growth have low heritabilities, when considered as a trait of the lamb. They are highly influenced by maternal genetic effects and non genetic effects such as litter size, date of birth and the environment. When studying hill sheep there are also problems obtaining accurate records of birth weights and early growth and it is normally impossible to obtain accurate measures of GL. Exploitation of the genetic variation in the traits BW, GL and early growth could be useful in breeding programmes to reduce early mortality and improve vigour in lambs.