A sheath assembly for an endoscope, the endoscope having a handle portion and an elongate scope portion extending from the handle portion to a tip, the sheath assembly comprising: an elongate tubular body extending along a longitudinal axis between a first distal end opening located at a distal end thereof and a first proximal end opening located at a proximal end thereof, the body comprising: a first wall section extending radially about the longitudinal axis to define a scope lumen, the scope portion of the endoscope being receivable coaxially in the scope lumen with the distal end of the body being disposed adjacent the endoscope tip and the proximal end of the body being disposed adjacent the handle portion of the endoscope; and a second wall section extending radially about at least a portion of the first wall section and longitudinally along the longitudinal axis between a second distal end opening adjacent the first distal end opening and a second proximal end opening adjacent the first proximal end opening, the first and the second wall sections (40,42) defining an integral collapsible suction lumen therebetween connectable in fluid communication with a first source of negative pressure; and a plug mated with the first distal end opening of the body for closing the scope lumen, the plug having a lens surface through which light or other energy is transmissible to or from the endoscope tip; characterised in that the body further comprises at least one rib member extending along the entire longitudinal axis, the at least one rib member extending radially within the collapsible suction lumen from a first end integral with one of the first and the second wall sections (40,42) to a second end disposed opposite the other one of the first and the second wall sections (40,42) and being bearable thereon to support the collapsible suction lumen when the first source of negative pressure is applied. an elongate tubular body extending along a longitudinal axis between a first distal end opening located at a distal end thereof and a first proximal end opening located at a proximal end thereof, the body comprising: a first wall section extending radially about the longitudinal axis to define a scope lumen, the scope portion of the endoscope being receivable coaxially in the scope lumen with the distal end of the body being disposed adjacent the endoscope tip and the proximal end of the body being disposed adjacent the handle portion of the endoscope; and a second wall section extending radially about at least a portion of the first wall section and longitudinally along the longitudinal axis between a second distal end opening adjacent the first distal end opening and a second proximal end opening adjacent the first proximal end opening, the first and the second wall sections (40,42) defining an integral collapsible suction lumen therebetween connectable in fluid communication with a first source of negative pressure; and a first wall section extending radially about the longitudinal axis to define a scope lumen, the scope portion of the endoscope being receivable coaxially in the scope lumen with the distal end of the body being disposed adjacent the endoscope tip and the proximal end of the body being disposed adjacent the handle portion of the endoscope; and a second wall section extending radially about at least a portion of the first wall section and longitudinally along the longitudinal axis between a second distal end opening adjacent the first distal end opening and a second proximal end opening adjacent the first proximal end opening, the first and the second wall sections (40,42) defining an integral collapsible suction lumen therebetween connectable in fluid communication with a first source of negative pressure; and a plug mated with the first distal end opening of the body for closing the scope lumen, the plug having a lens surface through which light or other energy is transmissible to or from the endoscope tip;