The loss of tightness of bolted flanged joints is primarily due to the relaxation of the joint; in particular, the clamping load is affected by the amount of relaxation that a gasket exhibits over time. Test methods are available for evaluating the ability of a gasket to maintain a given compressive stress. It is necessary, however, to evaluate the response of the joint members to a small change in gasket thickness produced by the effect of creep-relaxation. This paper presents an analytical evaluation of the effect of gasket creep-relaxation on the remaining gasket stress taking into account the flexibility of all joint members, thus allowing the evaluation of the required tightening load on the gasket. The results obtained by this approach are shown to agree with those determined finite on an experimental rig made up of 4-in. class-600-lb pair of flanges. Axisymmetric finite element models of larger flange assemblies are also used for comparison. The results show that creep-relaxation of gaskets has a major influence on the remaining compression load on the gasket.