AdiseasetransmissionmodelofSIStypewithstagestructureandadelayisformulated.Stabilityofthediseasefreeequilibrium,andexistence,uniqueness,andstabilityofanendemicequilibrium,areinvestigatedforthemodel.Thestabilityresultsarcstatedintermsofakeythresholdparameter.Theeffectsofstagestructureandtimedelayondynamicalbehavioroftheinfectiousdiseaseareanalyzed.ItisshownthatstagestructurehasnoeffectontheepidemicmodelandHopfbifurcationcanoccurasthetimedelayincreases.
