Genetic parameters for semen and litter size traits were analyzed using animal model analyses. Data were available from 122859 litters of 38895 Czech Large White and Landrace sows and from 88478 ejaculates of 1619 boars of the same breeds. All calculations were carried out separately for each breed. Among the semen traits, semen volume showed the highest heritability (0.20 to 0.25), followed by sperm concentration with a heritability of 0.18. The heritabilities of the remaining four traits (motility, percentage of abnormal sperm, total number of sperm and number of functional sperm) were around 0.10. There was a tendency for increasing litter size to be associated with slight decreases in the total number of sperm and in the number of functional sperm, especially in the Large White breed (genetic correlations -0.08 to -0.14 and -0.16 to -0.31, respectively). Some of the correlations between semen and litter size traits (especially with the percentage of abnormal sperm) were breed-specific.