We investigated the impact of the 2006 Massachusetts health care reform on insurance coverage and stability among minority and underserved women. We examined 36 months of insurance claims among 1,946 women who had abnormal cancer screening at six community health centers pre-(2004-2005) and post-(2007-2008) insurance reform. We examined frequency of switches in insurance coverage as measures of longitudinal insurance instability. On the date of their abnormal cancer screening test, 36% of subjects were publicly insured and 31% were uninsured. Post-reform, the percent ever uninsured declined from 39% to 29% (p .001) and those consistently uninsured declined from 23% to 16%. To assess if insurance instability changed between the pre- and post-reform periods, we conducted Poisson regression models, adjusted for patient demographics and length of time in care. These revealed no significant differences from the pre- to post-reform period in annual rates of insurance switches, incident rate ratio 0.98 (95%- CI 0.88-1.09). Our analysis is limited by changes in the populations in the pre- and post-reform period and inability to capture care outside of the health system network. Insurance reform increased stability as measured by decreasing uninsured rates without increasing insurance switches.