In 2003, Pennsylvania repealed its universal helmet law. If you're over 21 and you have more than two years' riding experience, you can now ride without a helmet in Pennsylvania. The authors of a paper to be published in the August 2008 issue of the American Journal of Public Health found a 32% increase in head injury deaths and a 42% increase in head injury-related hospitalizations in the two years after the helmet law was repealed -- and that's after taking into account the increase in motorcycle registrations. A University of Pittsburgh press release summarizes the finding of the report, "Changes in Motorcycle-Related Head Injury Deaths, Hospitalizations,and Hospital Charges Following Repeal of Pennsylvania’s Mandatory Motorcycle Helmet Law," was co-authored by Kristen J. Mertz and Harold B. Weiss of the Department of Neurological Surgery at the University of Pittsburgh.
According to an article in Hanover, PA's Evening Sun, 20 states have laws requiring all motorcycle riders to wear helmets, while 27 states have laws that require minors or passengers to wear head protection. Iowa, Illinois and New Hampshire have no helmet laws.