Abstract: The invention provides a mid-wheel drive wheelchair assembly (10) which includes a central base frame (11), a seat frame (12) removably attached to the base frame (11), a pair of transversely spaced leading pivot arms (13, 14) pivotally attached to opposite sides of the base frame respectively for pivotal movement about a common transverse pivot axis (17), a pair of ground engaging mid-drive wheels (19, 20) each mounted adjacent the trailing end of a respective side pivot arm (13, 14), a pair of ground engaging front castor wheels (21, 22) rotatably mounted at the leading ends of the pivot arms (13, 14), and a pair of ground engage rear castor wheels (23, 24) rotatably mounted at opposite ends of a rigid transverse port arm (25) which itself is pivotally mounted to the rear of the base frame (11) centrally thereof.