OBJECTIVES: Concerns have been raised regarding growth in advanced diagnostic imaging use.  This study evaluated national outpatient MRI/CT utilization rates during 2000-2009 and factors associated with imaging utilization. METHODS: This retrospective database analysis used data on all respondents in the nationally representative U.S. Medical Expenditure Panel Survey (MEPS) during 2000-2009.  Visits involving advanced diagnostic imaging were identified based on self-reported use of MRI or CT tests at    emergency rooms, office-based medical providers, and outpatient departments. The imaging utilization rate was defined as the number of outpatient visits with MRI/CT per 1,000 person-years.  Results were weighted to create nationally representative estimates at the person-year level for each year and the pooled 10-year period.  A multivariate logistic regression was estimated to identify predictors of imaging use.  RESULTS: A total of 319,246 person-years were included in the analysis.  MRI/CT utilization rates increased from 64.3 to 109.1 per 1,000 person years from 2000 to 2009, with older persons, females and Medicare enrollees having higher rates of use.  Growth in imaging slowed in recent years; the average annual decline in the imaging growth rate was larger than that for all outpatient services (4.7% vs. 0.9%).  The percentage of respondents with MRI/CT use (6.7% during 2000-2009) also increased at a slower rate in later years and declined during 2007-2009.  The average number of MRI/CT visits among imaging users was steady at about 1.5 visits during 2000-2009.  Age, female gender, white race, HMO participation, and all payer types (vs. uninsured) were significant predictors of imaging use.  Compared to 2005, years 2000-2003 were associated with a significantly lower likelihood of imaging use , while years 2004-2009 were not significantly associated, suggesting a slow-down in later years. CONCLUSIONS: Growth in advanced imaging utilization appears to have slowed in recent years, a finding of potential interest to policy-makers and payers.