An orthosis walking boot includes a posterior plastic shell with an open foot supporting portion extending outward from an integral open vertical leg extension to support a user's foot and leg and an anterior plastic shell with a horizontal foot covering portion for overlapping and covering the open foot supporting portion of the posterior shell and an integral open vertical leg extension for positioning within the posterior open vertical leg extension of the posterior shell. A two layer foam posterior liner extends upward within the posterior shell open vertical leg extension to receive the user's leg and adjustable fastening units secure the anterior shell to the posterior shell. An alternative orthosis walking boot with integrally attached foam liners on the posterior plastic shell and the anterior plastic shell is provided.