Megan McArdle argues persuasively in the Atlantic that lacking health insurance does not increase  mortality rate and the numbers thrown about to suggest otherwise are poppycock:

The possibility that no one risks death by going without health insurance may be startling, but some research supports it. Richard Kronick of the University of California at San Diego's Department of Family and Preventive Medicine, an adviser to the Clinton administration, recently published the results of what may be the largest and most comprehensive analysis yet done of the effect of insurance on mortality. He used a sample of more than 600,000, and controlled not only for the standard factors, but for how long the subjects went without insurance, whether their disease was particularly amenable to early intervention, and even whether they lived in a mobile home. In test after test, he found no significantly elevated risk of death among the uninsured.

This result is not, perhaps, as shocking as it seems. Health care heals, but it also kills. Someone who lacked insurance over the past few decades might have missed taking their Lipitor, but also their Vioxx or Fen-Phen. According to one estimate, 80,000 people a year are killed just by "nosocomial infections"-infections that arise as a result of medical treatment. The only truly experimental study on health insurance, a randomized study of almost 4,000 subjects done by Rand and concluded in 1982, found that increasing the generosity of people's health insurance caused them to use more health care, but made almost no difference in their health status.

If gaining insurance has a large effect on people's health, we should see outcomes improve dramatically between one's early and late 60s. Yet like the Kronick and Rand studies, analyses of the effect of Medicare, which becomes available to virtually everyone in America at the age of 65, show little benefit. In a recent review of the literature, Helen Levy of the University of Michigan and David Meltzer of the University of Chicago noted that the latest studies of this question "paint a surprisingly consistent picture: Medicare increases consumption of medical care and may modestly improve self-reported health but has no effect on mortality, at least in the short run."