The tolerance analysis aims to check if the tolerances specified on mechanism components allow to respect the assembly and functional requirements. Several papers illustrate that the form defects have an impact on the mechanism behavior, but most tolerance analysis techniques neglected them. To perform the tolerance analysis, three issues must be addressed: the geometrical deviations modelling, the geometrical behavior modelling and the technique of tolerance analysis. Therefore, this paper presents one contribution for each issue to perform tolerance analysis of over-constrained mechanism with form defect: • Modal representation of the form defect • Behavior modelling technique of the contact with form defect • Tolerance analysis technique with the integration of the different contact types.