The interaction-induced changes in the (3)He shielding constant of the helium dimer have been calculated using the full configuration interaction method and large basis sets. From these data the first virial coefficient for the (3)He isotropic shielding constant in gaseous helium has been determined. At room temperature it is negligibly small, approximately -0.006 cm(3) mol(1) and it increases monotonically with temperature. This behaviour is caused by the monotonic dependence of the isotropic shielding constant of He(2) on the interatomic distance. In addition, the non-relativistic value of the shielding constant of the isolated He atom was estimated to be sigma(iso) = 59.932 ppm.