NMR transitions are detected by electron nuclear double resonance at 4.2 K in a single crystal of doubly deuterated dl-serine. Quadrupolar splittings are measured from spectra acquired at 5° intervals in three orthogonal planes. From the angular dependence of these splittings, the quadrupole tensor and the orientation of the principal axis system with respect to the crystal axes are determined for the methylene deuterons. The relationship between the C-D bond length and the quadrupole coupling constant is discussed. In general, based on data available to date, one might expect the typical methylene bond length to lie in the range of 1.095 ± 0.010 Å and the quadrupole coupling constant to lie in the range 170 ± 10 kHz.