BACKGROUND: Cross-sectional data suggest that changes in health insurance status are associated with expenditures. No national longitudinal analysis has examined this relationship. OBJECTIVE: To evaluate the association between changes in health insurance status and expenditures. DESIGN: Cohort analyses using the 2000 to 2003 Medical Expenditure Panel Surveys. SETTING: U.S. civilian noninstitutionalized population. PARTICIPANTS: Three 2-year cohorts that included 20,848 adults age 21 to 64 years who were stratified by insurance type (private, public, military, or none): 17,130 participants were insured in both years, 342 participants were insured in year 1 and were uninsured in year 2, 385 participants were uninsured in year 1 and were insured in year 2, and 2991 participants were uninsured in both years. Persons who were insured for longer than 2 months but less than 10 months or who switched insurance type were excluded (n = 4039). MEASUREMENTS: Annual health care expenditures (any or none; amount, contingent on any expenditure; and the difference between year 1 and year 2). RESULTS: Adjusted expenditure probabilities were similar among all participant groups while insured and were higher than those for all participant groups while uninsured: 92.1% (95% CI, 91.4% to 92.7%) in year 1 and 91.8% (CI, 90.9% to 92.5%) in year 2 for persons insured in both years, 74.2% (CI, 71.7% to 76.5%) in year 1 and 74.8% (CI, 72.1% to 77.4%) in year 2 for persons uninsured in both years, and 90.7% (CI, 87.1% to 93.4%) for persons insured in year 1 and 74.6% (CI, 69.4% to 79.2%) for persons uninsured in year 2. The pattern was also consistent for the group that was uninsured in year 1 but insured in year 2. Adjusted annual expenditures among all participant groups with insurance were similar; expenditures among participant groups without insurance were similar but were lower than those among participants with insurance. Consistent differences in expenditures between year 1 and year 2 were observed for all groups. LIMITATION: Few participants changed insurance status. CONCLUSION: Changing insurance status is associated with changes in expenditures to levels that are similar to those for persons who are continuously insured or uninsured.