The government of Taiwan introduced universal health insurance to cover all citizens in 1995. This national health insurance program was proposed to assure the accessibility to health care at reasonable cost. Evaluation of the consequences, including health care utilization and expenditure, is crucial for policy adjustment. To evaluate the effect of Taiwan's national health insurance on health care utilization. Cohort survey conducted before and after the implementation of the national health insurance program. A total of 1021 randomly selected Taiwanese adults. Physician visits in the 2 weeks prior to the survey and hospital admissions and emergency department visits in the immediate past year. After the introduction of universal health insurance, the newly insured consumed more than twice the amount of outpatient physician visits (0.21 vs 0.48, P<.05) and hospital admissions (0.04 vs 0.11, P<.05) than before universal health insurance was implemented, bringing them to the same amount of health care contacts as the previously insured group. The newly insured also experienced an insignificant increase in emergency department visits. In contrast, the previously insured group had a small but statistically significant increase in outpatient visits (0.48 vs 0.59, P<.05) and insignificant changes in hospital admissions and emergency department visits. The universal health insurance removed some barriers to health care for those newly insured. The copayment design in the insurance scheme seemed to have an insignificant effect on curbing medical care utilization. Taiwanese health policy analysts should seriously consider the growth of health care expenditures since the implementation of universal health insurance.