OBJECTIVES: In July 2000, Florida replaced a Federal law mandating all motorcycle riders to wear helmets with a state law requiring helmets only for those < 21 years, or with under $10,000 health insurance. Hospitalizations for motorcycle accident-related injuries prior to and after the law changed were examined to understand potential consequences. METHODS: Florida hospital databases for 13 quarters prior to January 4, 1997 - June 30, 2000) and after the change July 1, 2000 - Septemebr 30, 2003), and published Florida motorcycle crash statistics were examined. Hospitalized cases with crash-related injuries were identified by via Emergency Department, ICD-9 diagnosis and E codes (E810.2-E825.2, E810.3-E825.3). Injury type, demographics, costs, length of stay (LOS) and disposition were analyzed. Charges (accommodations and ancillary services) adjusted by a 0.46 cost-to-charge ratio and appropriate inflation indices are reported as costs (2005 US$). RESULTS: In the pre-repeal period, 3914 inpatient motorcycle-related injury cases were identified (males: 86%; mean age: 35.6, mean LOS: 6 days); 6424 cases in post-repeal period (males: 87%, mean age: 36.4, mean LOS: 6 days); due to a rise in reported motorcycle crashes (33%), all related-injuries (44%) and deaths (66%) during 1997-2003; however, broader E-code use may also be a factor. Among hospitalized cases, there were significantly (p<0.01) more head, neck and cervical spinal cord injuries (45% vs 35%), and deaths (2.9% vs. 2.2%) post-repeal. Although average LOS did not increase, average cost per day ($4,093 vs. $3,359), and per stay ($20,502 vs. $17,243) increased significantly (p<0.01) post-repeal. Cumulative cost of inpatient care for motorcycle-related injuries rose from $68 million to $132 million during this period. CONCLUSIONS:Since universal helmet requirements were relaxed, there has been a substantial increase in motorcycle accident-related injuries overall, head injury hospitalizations, and injury-related deaths. Beyond clinical and societal consequences, these increases reflect an increased economic burden as well.