OBJECTIVES: Uninsurance has been shown to reduce health care utilization, but this effect may vary by uninsurance duration. Moreover, some argue that attitudes toward health insurance and medical care confound the association between uninsurance and utilization, but are rarely examined because they are often unobserved. This study examined the effects of uninsurance duration on prescription medication (RX) and emergency department (ED) utilization after adjusting for individuals’ attitudes towards healthcare and health insurance in US nonelderly adults. METHODS: Pooled data from panels 9 to 14 of the MEPS longitudinal data files (2004-2010) were used. Uninsured individuals were categorized by duration of uninsurance as 1-5, 6-11, 12-23 months and >=2 years and were compared to two-year privately and two-year publicly insured individuals. Four attitudinal responses were explored, including acknowledgement that one is more likely to take risks than the average person and beliefs that one is too healthy to need insurance, that insurance is not worth the cost, and that one is able to overcome illness without professional help. Zero-inflated Poisson and zero-inflated negative binomial models were applied using complex survey design correction in STATA 12 to adjust for differences in sociodemographic characteristics and health status. Results were reported as incidence rate ratios with 95% confidence intervals. RESULTS: Compared to two-year privately insured, individuals who were uninsured >=6 months used fewer RXs, and the reduction increased with uninsurance duration. All uninsured categories had more ED visits compared to two-year privately insured with no clear trend by duration. Including attitudinal variables had negligible effect on estimates of uninsurance. Those disagreeing with the attitudinal responses were found to utilize more RX; only those who disagreed with being able to overcome illness without help were found to have increased ED utilization. CONCLUSIONS: Uninsured had fewer prescription drugs but more ED visits. Attitudes towards insurance and medical care did not confound uninsurance effect.