The lattice parameters a, b and c of TmCu2 have been measured in the temperature range from 4.2 K up to 300 K using X-ray powder diffraction. The influence of the crystal field on the thermal expansion in TmCu2 in the paramagnetic region has been determined by comparing the thermal expansion of the non-magnetic YCu2 with that of TmCu2 (TmCu2 orders magnetically at TN=6.3 K). The data thus obtained are compared with a theoretical model given by Gratz et al. in 1993 using a set of crystal field parameters published by Gubbens et al. in 1992. From this analysis we get information about the unknown elastic and magnetoelastic properties of TmCu2.