A Monte Carlo study of the azimuthal angular distribution
around the virtual boson-proton beam axis for dijet events
in DIS at HERA is presented.
In the presence of typical acceptance cuts on the jets in the
laboratory frame, the azimuthal distribution
is dominated by kinematic effects rather than the
typical $\cos\phi$ and $\cos 2\phi$ dependence
predicted by the QCD matrix elements.
This implies that the $\phi$ dependent part
of the QCD matrix elements contributes even to the dijet production
cross section. Neglecting this $\phi$ dependence
leads to an error of about 5-8\% in the production cross
section for typical acceptance cuts in the laboratory frame.
We also present first NLO results on the $\phi$-decorrelation
of the jets through NLO effects.
