Health services and associated costs for adults with intellectual and developmental disabilities (IDD) were nationally profiled and the predictors of high expense users statistically modeled. Using linked data from the National Health Interview Survey and Medical Expenditure Panel Survey for the years 2002 through 2011, the study found a mixed pattern of differences in rates of service use and costs when compared to the general population depending upon personal characteristics, health status, and type of health care service. Prescription medication costs were the primary driver of total health care expenditures for Americans with IDD. The presence of secondary chronic health conditions and poor mental health status were the consistent predictors of high expense users across types of health care. Study results are discussed in terms of implications for more nuanced evaluations of health care costs and need for recurring surveillance of health care for Americans with IDD in the years following passage of the Patient Protection and Affordable Care Act.