Behavioral rating scales for dyskinesia in the non-human primate are frequently used to assess the efficacy of new treatments and to provide a clinical correlative with neurochemical and neuropathological changes. Although a large variety of different scales have been used in non-human primate studies, there is no single standardized scale, and none have been evaluated for reliability and validity. We are reporting a new global non-human primate dyskinesia rating scale (GPDRS) for the squirrel monkey, developed in the context of an independent study of dyskinesia. In this report we demonstrate the reliability and validity of this scale. The GPDRS is a single-item scale with well-defined points and brevity allowing for rapid and easy application for assessing the overall degree of dyskinesia. In this study, seven MPTP-lesioned and four non-lesioned (control) non-human primates were videotaped following treatment with either levodopa or water. To test inter- and intra-rater reliability, three examiners rated the videotape independently at two different time points and these assessments were compared. The validity of the scale was tested in two phases. First, examiners rated the videotape using the GPDRS and the Abnormal Involuntary Movement Scale (AIMS), a scale commonly used to rate dyskinesia in the non-human primate, and the ratings from each scale were compared. Second, validity was tested in the context of an independent dyskinesia study, in which the scale was used to distinguish between two treatment groups. The GPDRS was shown to have high inter- and intra-rater reliability and to be valid for the assessment of dyskinesia in the squirrel monkey. In this report we also demonstrate the inter- and intra-rater reliability of the AIMS. © 2001 Movement Disorder Society.