Similar to the state of the broader intellectual disabilities field, many gaps exist in the research and treatment of mental health concerns in people with Down syndrome. This review summarizes key findings on the type and prevalence of behavior and emotional problems in children, adolescents, and adults with Down syndrome. Such findings include relatively low rates of severe problems in children, and well-documented risks of depression and Alzheimer's disease in older adults. The review also considers emerging data on autism, and the paucity of studies on adolescents. Three next steps for research are highlighted, including a need to: (1) connect research on psychiatric status and diagnoses across developmental periods, including adolescence, and to examine such associated processes as sociability, anxiety and attention; (2) unravel complicated biopsycho-social risk and protective factors that serve to increase or diminish psychopathology; and (3) identify evidence-based treatments that both reduce distressful symptoms and enhance well-being in individuals with Down syndrome. (Contains 1 table.)