The proportion of the United States population without health insurance continues to grow. How will this affect the health of the nation? Prior research suggests that the uninsured are at risk for poor health outcomes. They use fewer medical services and have higher mortality rates than do insured persons. The episodic nature of uninsurance and its prevalence among disadvantaged groups makes it difficult to ascertain the health effects of uninsurance. The goal of this review is to assist researchers and policy makers in choosing methodologies to assess the effects of uninsurance. It provides a compendium of methods that have been used to examine the health consequences of uninsurance, the populations in which these methods have been used, and the strengths and weaknesses of different approaches. The review highlights the need for more longitudinal studies that focus on community-based samples of the uninsured.