A system is provided to monitor, over time, one or more physical variables related to a severity or progression of a movement disorder and/or of symptoms thereof. The monitored physical variables can include speech sounds; keyboard outputs; or accelerations, rotations, or other properties of the motion of one or more body parts. The system operates to detect, based on the monitored one or more physical variables, potential changes in the degree and/or character of the movement disorder symptoms. In response to detecting such a potential change, the system provides the user with one or more tasks that the user can perform. The system detects one or more properties of the user's performance and, based on that detection, determines the severity or progression of the movement disorder. The tasks can include stepping, turning, standing, sitting, reaching, typing, pointing, manipulating an object, speaking into a microphone, or other tasks.