This report, updated in 2009, examines the trend of uninsured young adults and offers strategic policy solutions to extend coverage to this population. 

From the report:

Young adults ages 19 to 29 are one of the largest segments of the U.S. population without health insurance: 13.2 million, or 29 percent, lacked coverage in 2007. They often lose coverage at age 19 or upon high school or college graduation: nearly two of five (38%) high school graduates who do not enroll in college and one-third of college graduates are uninsured for a time during the first year after graduation. Twenty-six states have passed laws to expand coverage of dependents to young adults under parents' insurance policies. Congressional proposals to reform the health system could help uninsured young adults gain coverage and prevent others from losing it. This is the seventh edition of Rite of Passage, first published by The Commonwealth Fund in 2003.

Full report: Why Young Adults Become Uninsured and How New Policies Can Help (PDF | 1.14 MB)

The Commonwealth Fund. (2009). Rite of passage? Why young adults become uninsured and how new policies can help, 2009 update. Nicholson, J. L., Collins, S. R., Mahato, B., Gould, E., Schoen, C. & Rustgi, S. D.