Domesticated reindeer livestock is an important resource for traditional economy of the indigenous peoples of the Russian Arctic. The article analyses the variability of the reindeer number trends in different Arctic regions and the reasons why reindeer livestock increases in some areas and decreases in others. The analysis is based on the official statistics data and scientific literature. Author argues that the key condition for the success of traditional reindeer husbandry is the informal economic environment. Due to peculiarities of the regional politics and the ways of adaptation of indigenous communities, such environment have been formed only in four municipal districts in the tundra of Western Siberia. In all other territory of the Russian Arctic the number of domesticated reindeer decreases or fluctuates at about the same level.