The National Health Insurance (NHI) in Taiwan has been implemented since March, 1995, however, little has been done on the effects of NHI on people's utilization and preference in choosing health care. Purpose: The purpose of this study was to examine the changes of the first choice of health care, outpatient visits and the factors associated with the outpatient visits before and after the implementation of the NHI. Data: Data and subjects, older than 19 years of age, for this study came from two Taiwan National Health Interview Surveys completed in 1994 and 2001. Demographic characteristics, health behaviors, self-perceived health, first choice of seeking care when not feeling well, and outpatient visits in the past two weeks were analyzed. Results: Our results showed that the percentage of those who preferred to see the doctor increased from 66% to 75% and that of those who preferred to buy over-the counter drugs decreased from 16% to 5 % from 1994 to 2001. Although the overall utilization increased from 1994 to 2001, those who preferred physician as their first choice did not use more health care in 2001. For those who did not consider physicians as their first choice, 21% of them did use the outpatient care in 2001, while only 14% of them did in 1994. Preference was an important factor associated with outpatient visits, additional factors were living in rural area, females, married, older age (> 65 years), self-perceived health as poor, and with chronic diseases in both surveys.