This study used unduplicated Medicaid enrollment records from 2005 to 2007 to examine enrollees' migration across states. Over the study period, only 3.7 percent moved to another state at least once. This provides a benchmark for adjusting national Medicaid statistics to reduce over-counting. Most moves were not associated with enrollment gaps, but 8.2 percent of moves were associated with short-term gaps. These gaps could indicate a lack of health insurance coverage, leading to concerns about patients' outcomes and higher systemwide costs.