A study of the relationship between litter size and other reproductive traits in Dutch Kooiker dogs born between 1956 and 1990 is described. The characteristics investigated were: litter size, homozygosity of the litter, paternal and maternal homozygosity, paternal and maternal litter size, paternal and maternal age, maternal parity, the year of birth, and interactions between these factors. A Poisson model with identity link was used. A negative effect on litter size was found for homozygosity of the litter (-3.175) and for maternal age. Positive effects on litter size were found for maternal litter size (+.09786) and maternal parity (+.5847, parity 2; +.8756, parity 3; +1.044, parity > or = 4). The effects of paternal age, paternal litter size, maternal homozygosity, and expected interactions were not significant. The positive effect of paternal homozygosity (+2.30) may have been caused by the frequent use of a small number of related sires.