The reasons of high mortality and of low life expectancy among Russian citizens as well as their sharp fluctuations observed in the 90-ies were explained differently by researchers, however, no attempt was made to analyze the impact made by a huge inflow of immigrant from the republics of the former USSR and "close abroad" in any case studies. In this paper we point at the fact that the mortality statistics and life expectancy in Moscow were influenced, at least for as long as 12 years, by a systemic error, which made the mortality index higher and the life expectancy lower, among Muscovites, due to overestimates of the absolute number of died Muscovites and to underestimates of the city residents. The 2001 life expectancy of men and women in Moscow calculated on the basis of data, from which non-residents who died in the capital were deleted, was 64.7 and 75.0, respectively, but not 61.7 and 73.5 as represented by the official statistics. The maximum negative effect of death cases of non-residents exerted on the life expectancy coincides with the overall mortality peak value in Moscow: life expectancy of Muscovites for 1994 estimated without accounting of the mortality rate for non-residents turned out to be 3.2 years higher for men and 1.5 years higher for women. Supposedly, the Russian mortality statistics is not nation-wide in line with the actual state of affairs. However, the influence of the discussed systemic error in Russia's regions can be expected to be less pronounced since the level of immigration in Moscow is most probably by far higher.