A pedigree file of 382831 Holstein cows and bulls, collected from herds registered by Animal Breeding Center of Iran during 1967 to 1999, was used to calculate the inbreeding coefficient. The mean inbreeding coefficient for the whole population (male and female), on a base year of 1946, was 0.184%. The means for cows (94 percent of the whole population) and bulls (6 percent of the whole population) were 0.180% and 0.240%, respectively. Minimum inbreeding coefficient was zero, while the maximum values were 39.844, 39.844, and 25.780 for the whole population, cows and bull populations, respectively. In this population 9.5, percent of animals were inbred with a mean inbreeding coefficient of 2.175%. The regression coefficients of inbreeding on year for the whole population and for the population of cows were similar and positive (0.021%). This regression was positive for bulls but higher than that for the population of cows (0.026%).