The authors assessed available prevalence information regarding neuropsychiatric conditions among adults with Down syndrome (DS) and compared these findings among adults with other intellectual disability (non‐DS). The study entailed a survey of 291 adults with DS living in Ohio (USA). Twenty‐three percent of adults with DS reported having a co‐occurring psychiatric disorder, a smaller than the reported occurrence of such conditions in the general adult intellectual disability population. Depression, anxiety disorders, and dementia or Alzheimer's disease were the most frequently reported neuropsychiatric disorders by adults with DS. The likelihood of experiencing a psychiatric disorder increased with age but did not vary by sex among adults with DS. Lower rates of problem behavior were reported in adults with DS compared to adults with intellectual disability (non‐DS). The authors' findings indicate that adults with DS may present different rates and types of co‐occurring psychiatric disorders than the larger population of adults with other intellectual disability. These findings warrant additional research and could provide critical information for planning and intervention.