The electron spin resonance (ESR) spectrum of the radicals derived from glycine in aqueous solution has not been reproduced satisfactorily until now, even by refined quantum mechanical approaches. Here we will show that a recently developed computational tool provides, instead, results in remarkable agreement with experiment. The computational protocol is based on density functional calculations, on the simulation of the solvent with a continuous dielectric description, and on averaging over the most important vibrational motions. Both the direct polarization and the geometry relaxation induced by the solvent on the glycine radical are analyzed, and their effect on the ESR spectra is evaluated. The present procedure is able to separate the various intrinsic and environmental contributions and to provide useful insight to the structural study of large flexible radicals in solution.