This study investigated the effect of litter size and parity on birth weight, weaning weight and survival at weaning and also, the effect of variations of birth weight on number and weight of piglets weaned and on pre-weaning survival. This experiment was performed on 114 sows and their 851 piglets. All piglets were divided into two groups for litter size, parity and birth weight and the main analyses were based on weight groups. Litter size affected birth weight significantly (p<0.01), but parity did not affect this trait (p>0.05). Furthermore, birth weight was determined to affect weaning weight, the number weaned and survival at weaning (p<0.01). It was demonstrated that each unit increase in litter size reduces birth and weaning weight. It was also shown that birth weight is a determining factor for weaning weight and survival at weaning and that high variations in birth weight cause high variations in survival. © Medwell Journals, 2009.