Thailand is among one of the first non OECD countries to have successfully introduced a form of Universal Health Coverage (UHC) in 2002. This policy defines a natural experiment for the evaluation of the effects of public health insurance on health behaviours. In the present paper, we look at the impact of the Thai UHC on preventive activities, risky behaviours and healthcare consumption using data from the 1996, 2001 and 2003 Health and Welfare Survey of Thailand. We use double robust estimators combining propensity scores and linear regressions to estimate Difference-in-Differences (DD) and Difference in DD (DDD) models. Results offer important insights. First, previously uninsured men and women increased their preventive activities (check-ups) more than any other groups. At the same time, there is no evidence of either an increase in risky behaviours or a reduction of preventive efforts by the newly insured population. In other words, we find no evidence of ex ante moral hazard. Regarding healthcare consumption, we see that hospital admissions increased by 2% and outpatient visits increased by 13% due to the UHC. Overall, these findings imply positive health impacts among the Thai population who entered in the UHC.