Lambda polarization at COMPASS

New data on $\Lambda^{0}$ polarisation in semi-inclusive deep inelastic scattering have been collected by the COMPASS collaboration at CERN, using a beam of longitudinally polarised muons with an energy of 160 GeV. The $\Lambda$ polarisation was measured through the weak decay $\Lambda\rightarrow p\pi^{-}$. First preliminary results on longitudinal and transverse $\Lambda^{0}$ polarization will be presented. Instrumental acceptance effects on the measured polarization will be discussed comparing real data and Monte Carlo simulations.