The invention consists of an endoluminal prosthesis adapted for placement at a bifurcation site within the body. The stent or stent-graft may be constructed to have segments of differing structural properties. A section of the stent-graft may be constructed to have a single-lumen tubular stent member covering a multilumen graft member. The stent-graft may comprise at least two modular components adapted for in situ assembly. An extended cylindrical interference fit may be used to seal the modular components.