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We present HSTACS observations of the most distant radio galaxy known, TN J09242201 at z 5:2. This radio galaxy has six spectroscopically confirmed Ly-emitting companion galaxies and appears to lie within an overdense region. The radio galaxy ismarginally resolved in i775 and z850, showing continuum emission alignedwith the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z 4–5. The Ly emitters are sub-L galaxies, with deduced star formation rates of 1–10 M yr1. One of the Ly emitters is only detected in Ly. Based on the star formation rate of 3M yr1 calculated from Ly, the lack of continuum emission could be explained if the galaxy is younger than2Myr and is producing its first stars. Observations in V606i775z850 were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V606 break (z 5) galaxies with z850 < 26:5 (5 ), two of which are also in the spectroscopic sample. We compare the surface density of2 arcmin2 to that of similarly selected V606 dropouts extracted fromGOODS and the UDF parallel fields. We find evidence for an overdensity to very high confidence (>99%), based on a counts-in-cells analysis applied to the contro