The effects of the presence of the user on MIMO performance for wireless communications systems is investigated through measurements in a reverberation chamber. Measured results have demonstrated that despite a decrement on the envelope correlation coefficient, a degradation of both diversity gain and MIMO capacity are expected when the user is present. While the validity of the correlation coefficients for predicting MIMO performance is limited in the presence of the user, the effects have also been found to be strongly dependent upon frequency, antenna topology and user characteristics It has been demonstrated that the power absorbed in the user plays a more important role for MIMO capacity than the change on the correlation coefficients due to the user’s presence.