The first aim of this study was to estimate the genetic effects of the piglets and the sow on gestation length. The second aim was to estimate genetic correlations between gestation length, piglet survival and average piglet growth. It was concluded that in pigs, gestation length is influenced by the genotypes of both the piglets and the sow. Selection or longer gestation would probably improve piglet survival after birth as well as piglet growth. It might, however, also result in more stillborn piglets.