The different evolutionary paths followed by the galaxies along their lives are expected to leave an imprint in their sizes. Nevertheless, observationally the role that the environment plays on shaping the galaxies is still unclear. Taking advantage of the great statistics provided by SDSS data, we address this question using a mass-complete sample of 232000 objects. We study the stellar mass-size relation of galaxies in the field and in clusters in the nearby Universe. Our results show that galaxies are slightly smaller in high-density regions at a fixed stellar mass. This difference is of ˜7.5 per cent for late-type galaxies and ˜3.5 per cent for early-type galaxies. Moreover, the scatter of the relation is also smaller in clusters than in the field, with differences of ˜0.8 per cent for late-type galaxies and ˜3.5 per cent for early-type galaxies. These results point towards an earlier formation of the galaxies in high-density environments as well as to an evolution from a more homogeneous family of progenitors than those inhabiting less dense environments.