The hydrazidosilanes Ph2Si(NHNMe2)(2) (1), Me2Si(NHNMe2)(2) (2), PhSi(NHNMe2)(3) (3), MeSi(NHNMe2)(3) (4), PhClSi(NHNMe2)(2) (5), MeClSi(NHNMe2)(2) (6), Me2ClSi(NHNMe2) (7), MeClHSi(NHNMe2) (8), MeHSi(NHNMe2)(2) (9), Me2HSi(NHNMe2) (10), Me2NN[HSi(NHNMe2)(2)](2) (11) and Si(NHNMe2)(4) (12) have been prepared by the reaction of the corresponding chlorosilanes with N,N-dimethylhydrazine. Some of the compounds containing Si-Cl and N-H functions simultaneously (6, 7, 8) are very reactive and tend to polymerise and could only be characterised by spectroscopic methods (H-1, C-13, Si-29 NMR, IR, MS). All other compounds could additionally be characterised by elemental analyses. The structures of 1, 2, 5, 9, 11 and 12 in the solid state were determined by X-ray diffraction. These include the first structural determinations of compounds containing SiH-NH-N (9, 11) and SiCl-NH-N (5) units.