We present the results of a K-band imaging survey of 40 arcmin(2) in fields
around 14 radio-loud active galactic nuclei (AGN), comprising six radio ga
laxies and eight quasars, with z > 1.5. The survey, which is 80 per cent co
mplete to K < 19.2 mag and complemented by R-band imaging, aimed at investi
gating whether extremely red objects are present in excess around high-z AG
N, and to study the environment of z > 1.5 radio galaxies and radio-loud qu
asars. At 18 < K < 19 mag, the differential galaxy counts in our fields sug
gest a systematic excess over the general field counts. At K < 19.2 mag we
find an excess of galaxies with R - K > 6 in comparison with the general fi
eld. Consistently, we also find that the R - K colour distribution of all t
he galaxies in the AGN fields is significantly redder than the;colour distr
ibution of the field galaxies. On the other hand, the distribution of the R
- K colours is indistinguishable from that of galaxies taken from literatu
re fields around radio-loud quasars at 1 < z < 2. We discuss the main impli
cations of our findings and we compare the possible scenarios that could ex
plain our results.