The electron density and related properties of biguanidinium dinitramide (BIGH)(DN) and biguanidinium bis-dinitramide (BIGH(2))(DN)(2) crystals (space groups P (1) over bar and C2/c) have been determined from low-temperature (90(l) K) X-ray diffraction experiments. The Hansen-Coppens multipole model as implemented in the XD program gave R = 0.0247 and 0.0201 (all reflections) which allowed the calculation of the electron density and Laplacian distributions. The bonding (3,-1) critical points were also found. The analysis of the results shows that Bader's topological theory provides a more useful description of the chemical bonding in the studied crystals as compared to the classical analysis of deformation densities. The hydrogen bonding in the crystals was analyzed. The atomic charges were integrated over the atomic basins.