Background: Medication side-effects such as tardive dyskinesia (TD) are known to occur in individuals with a history of psychotropic drug use. This study aimed to contribute to the development of measures for assessing TD by examining the validity of the "Matson Evaluation of Drug Side-effects" (MEDS) with the "Dyskinesia Identification System: Condensed User Scale" (DISCUS) in 163 adults with intellectual disability (ID). Method: To establish convergent validity, the relationship between the MEDS and the DISCUS in identifying TD was examined. To establish divergent validity, the ability of the MEDS to differentiate between TD and other side-effects was investigated. Results: The MEDS demonstrated convergent validity with the DISCUS on the Central Nervous System-Parkinsonism/Dyskinesia (CNS-PD) Subscale. The MEDS showed divergent validity with the DISCUS in cardiovascular and gastrointestinal side-effects, Parkinsonism symptoms (i.e., tremor, mask-like face), dystonia, and akathisia. Discussion: The MEDS appears to have significant clinical utility in measuring tardive dyskinesia and other medication side-effects in individuals with ID. (Contains 6 tables.)