We performed first-principles molecular dynamics calculations at finite temperature, to study the interacting conformations of Lewis-X (LeX) trisaccharides in the crystalline phase. The calculated cell parameters and detailed atomic structure of the LeX molecule compare well to the experimental data obtained by X-ray diffraction. We identify and characterize the hydrogen-bond network, responsible for the mutual interaction of the LeX pairs, whereas we find the intramolecular conformation and stability to be mainly assured by dispersion forces. The relative contributions to the crystallization energy of the hydrogen bonds and of the dispersion forces are defined and quantified. From this study, candidate configurations for the fully hydrated, in vivo structures of homotypic LeX LeX interactions at cell surfaces can be proposed. We discuss how these configurations could also be relevant for the adhesion and self-assembly of nanostructures.