In order to make mechanisms work the presence of clearance in kinematic pairs may be unavoidable. As a major consequence position and orientation errors of the output link occur when loads are applied to the mechanism. This paper focusses on the effect of clearance on the dislocation of the pairing elements of the prismatic pair. A kinetostatic model of the prismatic pair with clearance is presented and contact modes of the pairing elements are found. A particular geometry of the prismatic pair is considered to illustrate the proposed approach which can be used, in principle, for any pair geometry. The proposed model may be implemented in kinematic, kinetostatic and dynamic analyses as well, for the purpose of computing the influence of clearance on position-orientation errors of any link of the mechanism. Finally a numerical example is reported.