The retraction of a cylindrical rigid indenter from a viscoelastic substrate is studied by means of an efficient Green's function method. Hysteresis is observed in the load to area relationship in accordance with experimental results. Although our model relaxes many assumptions posed by LEFM-based analytical theories, the results fall between the limits, at high and low retraction velocities, predicted by the theories. Approaching the high velocity instantaneous limit requires, however, very high velocities or Maugis parameter. The work of adhesion is found to change during retraction. A non-dimensional parameter is proposed to estimate the effect of viscoelasticity in adhesive hysteresis.