Within the last three decades, the study of conditions that co-occur with intellectual disabilities has flourished. The present paper provides an analysis of the content of 405 papers that were reviewed on the topic. From these papers, trends emerged. The papers fell into one of three broad categories; comorbid psychopathology, comorbid medical problems, and comorbid challenging behaviors. Also, the volume of studies has been increasing rapidly. Implications of these and related issues are discussed. (C) 2013 Elsevier Ltd. All rights reserved.