Most internists found more similarities than differences in caring for young adults with intellectual and developmental disabilities (I/DD) and elderly adults with dementia. Both populations require longer office visits and more staffing resources due to complex health histories. Obtaining records and coordinating care can be difficult for both. Reliance on advocates, community services for transportation and supervision, and vulnerability to insurance changes are also similarities. While specific diseases differ, models for geriatric care could potentially address supervision and caretaking needs for adults with I/DD. Strengthening safety net services would help low-income families and elderly patients with dementia or I/DD.