Context : HR 8799 is so far the only directly imaged multiple exoplanet system .
The orbital configuration would , if better known , provide valuable insight into the formation and dynamical evolution of wide-orbit planetary systems .

Aims : We present data which add to the astrometric monitoring of the planets HR 8799 b , c and d. We investigate how well the two simple cases of ( i ) a circular orbit and ( ii ) a face-on orbit fit the astrometric data for HR 8799 d over a total time baseline of \sim 2 years .

Methods : The HR 8799 planetary system was observed in L ^ { \prime } -band with NACO at VLT .

Results : The results indicate that the orbit of HR 8799 d is inclined with respect to our line of sight , and suggest that the orbit is slightly eccentric or non-coplanar with the outer planets and debris disk .

Conclusions :