A machine for forming a negative cast of an end portion of an amputated limb has an outer rigid tubular body an elastically deformable tubular membrane housed within the rigid tubular body and having its opposite annular end portions fluid-tightly connected to the rigid tubular body, to define a through-duct through which the limb passes and, with the rigid tubular body, a fluid-tight elongated annular chamber with variable volume surrounding the limb a reference membrane for positioning of the limb within the duct being provided at the outlet of the duct.
