In response to political pressure, the state of Florida repealed its mandatory motorcycle helmet-use law for all operators and passengers older than the age of 21, effective July 1, 2000. Using monthly data and a multiple time-series design, the authors assessed the effect of this law change on serious injury and fatality rates for motorcycle riders aged 21 and older. Controls for serious injury and fatality rates for motorcycle riders younger than 21 years of age were included in the analyses. Maximum-likelihood results showed that the repeal of the mandatory helmet-use law in Florida had little observable effect on serious injuries or on fatalities that resulted from motorcycle crashes. Policy implications of these findings are discussed, and explanations are given as to why the repeal of the mandatory motorcycle helmet-use law in Florida was inconsequential.