An increasing rate of artificial insemination leads to declining number of breading boars (sires) and often to number of genealogical lines. Thereby sires leave more female offspring at herds and the genetic similarity (degree of homozygosity) expressedby coefficient of relationship (Rxy) among dams is increasing. A simplified method based on number of sire lines, sires of dams, and dams within sires, where sows are granddaughters, half-sibs, and sibs, respectively, was used for estimating Rxy in sowsof Přeštice breed between 1995 and 2005. The average values of Rxy ranged from 2 to 3% during the observed period, which is favourable for small population of Přeštice breed.