This article explores the methods and results of the research of Muslim religiosity in the Middle Volga and Ural regions in the late Soviet Union. The article draws upon the sociological surveys conducted in 1966 – 1991. These surveys revealed some interesting trends that did not correspond to ideological objectives and expectations. The article also demonstrates regional specifics of the Soviet sociological school and its relationship with the ideological authorities. The surveys of religiosity of the Soviet population were, in a sense, a vote of confidence to the official ideology.