Matson and Nebel-Schwalm (Research in Developmental Disabilities 28(4) 341-352, 2007) conducted an overview of comorbid psychopathology with autism spectrum disorder (ASD) in children. The purpose of the current paper is to expand on Matson and Nebel-Schwalm (Research in Developmental Disabilities 28(4) 341-352, 2007) by discussing the relationship between comorbid psychopathology in ASD and other variables. The current paper will include research across the lifespan, from babies and toddlers to children, adolescents, and adults. Topics explored are the prevalence of comorbid psychological disorders, the importance of studying comorbid psychopathology, as well as the measures used to assess comorbid psychopathology in ASD. Research on the relationships between comorbid psychopathology in ASD and parental and sibling stress and well-being, developmental regression, language and communication, adaptive behavior, social skills, autism severity, challenging behavior, gastrointestinal symptoms, sleep problems, epilepsy, sensory issues, and quality of life is also discussed. Age-related variations in comorbid psychopathology are also examined. Finally, recommendations for treatment are given as well as areas where future research is needed.