An adjustable mouse includes a base portion including a flat bottom configured to rest on a flat surface and a curved top, a palm rest portion including a body configured to be contoured to fit a user's hand and a curved bottom that is configured to mate with the curved top of the base portion, and a mechanism configured to secure the palm rest portion to the base portion at a desired angle of tilt. The adjustable mouse further includes a thumb adjustment assembly coupled to the base portion. The thumb adjustment assembly is configured to move a thumb rest portion between a retracted position and an extended position.