The paper deals with the shear strength of prestressed hollow-core slabs determined by the theory of plasticity. Two failure mechanisms are considered in order to derive the solutions.In the case of sliding failure in a diagonal crack, the shear strength is determined by means of the crack sliding model developed by Jin-Ping Zhang. The model takes into account the resistance against formation of cracks due to prestressing as well as the variation of the prestressing force in the transfer zone.Due to the fact that the anchorage of the reinforcement takes place by bond, a rotation failure, which is induced by a crack formed at the support with subsequent slip of the reinforcement, is also considered. This failure mode is likely to occur in cases with a high prestressing force combined with a short shear span.The theoretical calculations are compared with test results from the literature. A good agreement has been found.