Psychopathology prior to the last four decades was generally viewed as a set of problems and disorders that did not occur in persons with intellectual disabilities (ID). That notion now seems very antiquated. In no small part, a revolutionary development of scales worldwide has occurred for the assessment of emotional problems in persons with ID. The first standardized test to emerge was the "Psychopathology Instrument for Mentally Retarded Adults" ("PIMRA") in 1984. Since that time, an impressive number of measures of general psychopathology have emerged for adults and children as well as for persons across the full range of levels of ID. The purpose of this review was to provide a description of available measures, to review papers published on these measures, and to discuss emerging trends in test development. The trends in this body of information for enhancing differential diagnosis of psychopathology in persons with ID are discussed. (Contains 2 tables and 1 figure.)