Background Lack of health insurance may adversely impact medication adherence and the control of cardiovascular risk factors. We examined if the association between insurance and LDL-C is due to self-reported low medication adherence. Methods This cross-sectional study included 8685 black and white men and women aged 45 and older who participated in the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort and used statins. Medication adherence was assessed using the 4-item Morisky Medication Adherence Scale (MMAS-4). Mean differences in LDL-C between participants with and without insurance were calculated using generalized linear models before and after adjustment for MMAS-4. Subgroups stratified by age, annual household income, diabetes, and CHD were compared. Separately, individual MMAS-4 questions were examined for mediation effects. Results After multivariable adjustment but without MMAS-4, LDL-C was 2.5 mg/dL (95% CI − 0.6, 5.6) higher among uninsured versus insured participants. After further adjustment for MMAS-4, LDL-C was 2.6 mg/dL (95% CI − 0.5, 5.6) higher. Stratified analyses produced similar results. No mediating effect was observed when each MMAS-4 question was examined separately. Conclusion High medication adherence does not mediate the association between having health insurance and lower LDL-C.