A combined scanning tunneling microscopy and low energy electron diffraction study enables to propose a model of the atomic arrangement in the first close-packed monolayer of Gd on W(110). The lattice parameter of the Gd/W(110) epitaxial system in the first two layers is larger than in the bulk Gd. This lattice mismatch amounts to 2% for the first and ca. 0.3% for the second monolayer. From the third monolayer on the lattice parameter corresponds to the one of the bulk Gd crystal.