The recent Sumatra earthquake and subsequent tsunami has provoked greater awareness of the hazard posed by coseismic fault displacement associated with sea-floor subduction zones. This catastrophic event has focused renewed efforts on tsunami forecasting, modeling, and detection. Yet the mechanism that causes this type of tsunami, coseismic fault displacement of a sea-floor subduction zone, is still treated deterministically. This paper describes a methodology for probabilistic fault displacement hazard analysis (PFDHA) for a sea-floor subduction zone, and presents example displacement hazard curves for the Cascadia Subduction Zone. The goal of this probabilistic methodology is to quantify the uncertainty and associated hazard of coseismic fault displacement of sea-floor subduction zones. This will provide tsunami modelers with a probabilistic measure of the occurrence of fault displacement, and decision makers with a rational basis for tsunami hazard mitigation measures.