Three-dimensional incommensurately modulated cubic lazurite from the Malo-Bystrinskoe deposit (the Baikal region) was studied by the methods of X-ray diffraction analysis. The a parameter of the cubic unit cell is 9.077(1) Angstrom. The calculations performed within the sp. gr. P23 (R = 0.056, 309 independent reflections) provided detailed information on the average structure of the mineral (the satellite reflections were ignored). (C) 2002 MAIK "Nauka/Interperiodica".