At 115 K, crystals of trisilylamine are triclinic, space group P, with a= 6.84, b= 8.17, c= 6.87 Å, α= 95.5, β= 119.1, γ= 98.6°(0.3% estimated standard deviations are assumed), and Z= 2. Crystals were grown in situ on a Weissenberg goniometer fitted with low-temperature equipment. The structure has been refined to R= 0.051 using 651 photographic (microdensitometer) intensities. There are no short intermolecular contacts. Deviations from molecular C3h symmetry are negligible, even for the hydrogen atoms. The mean length of the Si–N bonds is 1.730(5)Å. The heavy atoms vibrate mainly in a direction which is parallel to the molecular C3 axis.