OBJECTIVE: To explain variations in the magnitude of health care catastrophe and household impoverishment from out-of-pocket (OOP) payments in relation to differences in services and providers of health care during the pre- and post- universal health care coverage (UC) periods in Thailand. METHODS: Analysis of the national socio-economic surveys of household income and consumption in 2000 (N=24,747), 2002 (N=34,785) and 2004 (N=34,843). RESULTS: Households whose members being admitted to hospitals for in-patient (IP) experienced health care expenditure beyond a catastrophic level (defined as OOP payments more than 10% of total consumption) most frequently (31.0% during pre-UC period in 2000 and 15.1-14.6% during post-UC period in 2002-2004). The catastrophic incidence in households with OOP payments for out-patient (OP) without IP services was less frequent (12.0% pre-UC and 7.9-8.3% post-UC). The households paying OOP only for self medication faced the catastrophic expenditure by only 2.1% and 0.4-0.6% over the same period. Among the households at risk to health care catastrophe from IP service during the post-UC period, the catastrophic incidence varied from 32.1-27.8% for services by private hospitals, and 13.9-11.1% by provincial hospitals and 6.5-7.3% by district hospitals respectively. The variations in household impoverishment due to OOP health payments followed a similar catastrophic pattern. Paying for IP services accounted for the poverty increase by 95.6% and 84.0-71.5% of the impoverished households during pre-UC and post-UC periods, respectively. The relative increase in post-OOP impoverishment was found in 98.8-100% of those became poor from the payments to private hospitals regardless of type of health care services. CONCLUSIONS: Households making OOP payments for IP services and private hospitals were most likely to face the catastrophic health care expenditure and impoverishment.