The speech dysfunction of Parkinson's disease is complex and individually variable owing to the interaction of muscle rigidity, tremor and disturbance of movement. Eight speech dimensions which are characteristically disturbed in Parkinson's disease are discussed with reference to available research findings. In order to provide a more detailed description of the speech than could be obtained by clinical notes alone, a speech rating scale has been developed, and is presented in summarized form for clinical use. Incidence and progression of the speech dysfunction are considered in addition to the problems of assessment peculiar to the patient with Parkinson's disease.