OBJECTIVES: Radiologists claim that performing two or more CT scans in succession is rarely necessary, yet the practice of multiple CT scanning during the same visit has continued in recent years. The objective of this study is to review the evidence and identify factors contributing to this practice. METHODS: The retrospective study included patients from the US Medicare 2009 hospital database. Over 6 million outpatient claims with the following information were extracted: patient demographics, hospital characteristics, CT scans hospital charges and body parts associated with CT scan administration. Multi-level logistic mixed effects regression was conducted to identify significant factors associated with the overuse of CT scans among US hospitals. RESULTS: There were 690,643 Medicare patients that received multiple CT scans during a hospital outpatient visit in 2009. More than 664 hospitals that administered at least two scans on more than 30% of their Medicare outpatients. The national average was 5.4%. The figures show wide variation among states as well, from about 5% in Maryland to almost 23% in Oklahoma. After multivariable adjustment, female patients had a lower incidence rate of CT scan overuse (odds ratio, 0.850; 95% CI, 0.847 to 0.851, p<0.0001). Rural hospitals tend to practice more CT scan overuse (odds ratio, 1.835; 95% CI, 1.670 to 2.016, p<0.0001) than urban hospitals. Hospital charged patient costs of CT scans also tend to vary across regions. CONCLUSIONS: There is strong statistical evidence that US hospitals practice of CT scan overuse continued in 2009 based on the Medicare outpatient population. While the study is subject to limitations, it corroborates with previous policy studies that hospitals can and should do more to change physician behavior by implementing new protocols and continue to monitor ongoing administrations of multiple CT scans. The study also warrants potential investigation of similar European hospital databases.