The Black blazed sheep breed is a rare, native Dutch breed of sheep. In order to maintain such a small population it is of great importance to monitor the population size, the rate of inbreeding and kinship in the population. Pedigree data of the current population within the two studbooks, the Dutch Black blazed Studbook (Nederlands Zwartbles Stamboek, NZS) and the Black blazed breeders group (Zwartbles Fokkersgroep, FG) was analyzed. The population was analyzed in terms of number of animals, number of offspring and rate of inbreeding per generation. In addition, simulations were carried out, where the effect of exchange of animals between the two studbooks on the rate of inbreeding was predicted for the next 50 years. Currently 95% of NZS animals have NZS parents and about 5% of NZS animals come from parents of the FG studbook. Conversely, about 35% of the animals in the FG studbook have parental animals registered at the NZS and about 65% of the FG animals stay within this studbook. The analysis of 93,634 sheep in total (1987 - 2018) showed that the rate of inbreeding per generation was especially high in the last period from 2015 to 2018 (0.82%). This is well above the FAO standard of 0.5% per generation. The current exchange between the studbooks should certainly be maintained for the purpose of inbreeding management, and especially for the FG population it is necessary to use breeding animals from the NZS population