We present an assignment of the experimental O-17 NMR shielding parameters for L-glutamic acid(.)HCl (Lemaitre, V.; Pike, K. J.; Watts, A.; Anupold, T.; Samoson, A.; Smith, M. E.; Dupree, R. Chem. Phys. Lett. 2003, 371, 91) based on first-principles quantum mechanical calculations. We use density functional theory and the gauge-including projector-augmented wave method (Pickard, C. J.; Mauri, F. Phys. Rev. B 2001, 63, 245101), which treats the true periodic nature of the crystal structure. We perform further theoretical calculations on a range of glutamic acid polymorphs and draw general conclusions about the influence of hydrogen bonding on O-17 NMR shielding parameters.