Data from official dairy recording of Basque Country were used to compare two models of genetic evaluations: some of them, which included the effect of generic groups, and the other, not considering this effect. Those animals without known parents in the genealogy were asigned phantom parents, defined by their probable origin (unknown, Canada, USA, Europe and Spain), by the period of time in which their sons were born (unknown, until 1975 and between 1976 and 1992) and by their sex and the sex of the son (sire of bull, sire of cow, dam of bull, dam of cow and both). The objective of genetic groups is to account for genetic selection and genetic trend in this dairy population. The correlations between genetic values of females and males whith more than 15 daughter were calculated and genetic trends for these two groups of animals were also compared. The changes were observed specially in the bulls, what is logical because the lack of information is more important in the genealogy of males. The correlations were more than 0.96 for all the characters considered in cows and bulls whith more than 15 daughters, what indicates that the changes debt to the inclusion of genetic groups in the model of evaluation will not be generally drastic.