The text introduces new national database of diseases of dairy cattle cows, its practical use and shows the example of use in es­timation of breeding values of resistance to clinical mastitis. For successful evaluation of animals it is necessary to record animal performance, in the case of improvement of resistance to illnesses, occurrence of diseases. Other necessary information for eva­luation can be acquired from existing performance testing. For estimation of breeding values for clinical mastitis, records of 35 845 lactations of 15 822 Holstein cows from 7 farms from years 1996 to 2014 were utilized. The estimation of breeding values was done by linear animal model with pedigree matrix. The pedigree included 27 902 animals. The breeding values were estimated for clinical mastitis defined as occurrence during 305 day lactation: yes or no.