Factors affecting prolificacy and lambs rearing results in Olkuska sheep population. The aim of this study was to evaluate reproductive performance of the growing Olkuska sheep population and to analyse impact of a number of factors on lamb rearing results as well as the length of ewes’ utilisation in the flock. Although reproductive performance of Olkuska sheep is still at a relatively high level, recently a decrease of average prolificacy and the continuously low percentage of lambs reared have been observed. This might be related to the rapid growth of the population in the recent years and rather short flock-life of ewes, on average 3.17 years. The results of this study confirm that the size of the litter had the highest impact on lamb rearing results. Substantial differences in reproductive performance depending on the age of the dam were also observed. Despite of poor rearing of lambs born in large litters, no significant correlation between the average prolificacy of ewes in the flock and the percentage of lambs being reared was observed. The results indicate that a major influence on lamb rearing performance depends upon individual characteristics of a dam, as well as husbandry conditions in the flock and skills of the breeder.