Objective. - To describe Minnesota's health care system reform efforts and their implications for other state and national reform initiatives, document the rate of uninsurance in 1990 and 1995 with special attention to childrens' access to health insurance, and examine the effectiveness of MinnesotaCare, a voluntary state-subsidized health care plan, in serving its target population. Design. - Three cross-sectional telephone surveys: 2- stage random samples of Minnesotans of all ages in 1990 and 1995 and a stratified random sample of MinnesotaCare enrollees in 1994. Participants. - For the 2 statewide surveys, 10310 respondents participated in 1990 and 11519 in 1995; more detailed information was collected on approximately 1600 respondents in each survey. Eight hundred MinnesotaCare enrollees participated in the third survey conducted in 1994. Main Outcome Measure. - Changes in rates of uninsurance. Results. - While the rate of uninsurance increased at the national level, the point-in-time Minnesota rate remained stable and low at 6% between 1990 and 1995. The proportion of children uninsured for 12 months or more decreased from 5.2% in 1990 to 3.1% in 1995, while the proportion of uninsured single adults remained stable at approximately 11%. There was no evidence that MinnesotaCare enrollees are gaming the program, or that the program has resulted in significant erosion from the private market. Conclusions. - MinnesotaCare has enabled the state to maintain a low rate of uninsurance and has reduced this rate among its primary target: children. The program has been less effective in enrolling single adults, although it may be too early to witness the effects of recent expansions targeting this group. Minnesota's experience suggests that other state and national reform efforts aimed at reducing uninsurance, particularly among children, are likely to be successful.