The results of the study carried out in a gravity-arch dam to measure its seasonal movements with TLS are presented. These values are compared with radial movements of the dam crest recorded by direct pendulums. The results show differences, only few millimeters, being the best result one millimeter discrepancy. The factors that have been considered are the precision and accuracy of the equipment, distance and angle of incidence of the laser beam, the density of the point cloud and the size of the triangles of the meshes. Considerations about density of point clouds and size of triangular meshes are made. In this study, a 7 cm distance between points and a 20 cm mesh size have given good results. Finally, a methodology is proposed to compare by reference to one of the meshes.