A jaw exerciser for providing passive motion therapy such as that used to treat trismus is provided. The jaw exerciser has a user-adjustable distance between the upper jaw support and the lower jaw support. The jaw exerciser includes a shaft, a first or upper jaw support frame including a first jaw support, a second or lower jaw support frame including a second jaw support, a distance adjuster which may be in the form of a jack screw for manually adjusting the distance between the first jaw support and the second jaw support, and a retaining screw. The jack screw may be received by the second or lower jaw support frame and engage the first or upper jaw support frame. Removable bite pads may optionally be provided for installing on the first jaw support and the second jaw support.
