Investigations with 1248 newborn piglets in 7 farms showed a high significant influence of birth weight on parameters of early postnatal vitality. The duration between birth and first standing up was by two times, the time between birth and first udder contact by 3.5 times and the duration between birth and first colostrum intake was by 4 times longer in piglets with a low birth weight (< 800 g) in comparison with heavier piglets at birth (> 2200 g). The drop in rectal temperature up to 30 minutes after birth reached 4.5 Kelvin in lightweight piglets, whereas their litter mates with a high body weight at birth had a value of 0.85 K (p < 0.01). The birth weight of piglets belongs to the most important endogenous factors with influence on the vitality of newborn piglets and has a high prognostic value in relation to the risk of losses and the live weight development of neonates.