  We have analyzed galaxy properties in the environment of a sample of 70 Ultra
Steep Spectrum (USS) radio sources selected from the Sydney University Molonglo
sky Survey and the NRAO VLA Sky Survey catalogues, using near-IR data complete
down to Ks=20. We have quantified galaxy excess around USS targets using an
Abell-type measurement N0.5 (Hill & Lilly 1991). We find that most of the USS
fields studied are compatible with being Abell class 0 richness clusters. A
statistical analysis of the distribution of companion galaxies around USS radio
sources show a pronounced tendency for such objects to be found in the
direction defined by the radio axis, suggesting that they may be related to the
presence of the radio sources. We have also measure the central concentration
of light of the USS sample and compare these to the values obtained for field
galaxies and galaxies selected through other methods. By using Spearman
statistics to disentangle richnesses and concentration indices dependences, we
detect a weak, but significant, positive correlation. We find that at z > 2 USS
radio sources are more concentrated than field galaxies at similar redshifts,
indicating that these objects trace the most massive systems at high redshift.
