Examples of prostheses are provided having an internal branch. A tubular graft body of the prosthesis defines a main lumen extending between an inflow end and an outflow end of the graft body. A stent structure is coupled along the graft body. A trough is at least partially defined by a trough wall extending into the main lumen from a sidewall of the graft body. A side branch defines a branch lumen and extends from the trough within the main lumen towards one of the inflow or outflow ends of the graft body. A branch lumen facing surface of the trough wall is a continuous surface with an outer surface of the sidewall of the graft body. A boundary of the trough may be configured to provide a smooth transition surface between the trough and the sidewall.