  The luminosity-size and stellar mass-size distributions of galaxies out to
z~3 is presented. We use very deep near-infrared images of the Hubble Deep
Field South in the J_s, H, and K_s bands, taken as part FIRES at the VLT, to
follow the evolution of the optical rest-frame sizes of galaxies. For a total
of 168 galaxies with K_{s,AB}<23.5, we find that the rest-frame V-band sizes
r_{e,V} of luminous galaxies (<L_V>~2x10^{10}h^{-2}L_sun) at 2<z<3 are 3 times
smaller than for equally luminous galaxies today. In contrast, the mass-size
relation has evolved relatively little: the size at mass
<M_*>~2x10^{10}h^{-2}M_sun, has changed by 20(+-20)% since z~2.5. Both results
can be reconciled by the fact that the stellar M/L ratio is lower in the
luminous high z galaxies than in nearby ones because they have young stellar
populations. The lower incidence of large galaxies at z~3 seems to reflect the
rarity of galaxies with high stellar mass.
