Objectives. To evaluate the impact of the partial repeal of Michigan’s universal motorcycle helmet law on helmet use, fatalities, and head injuries. Methods. We compared helmet use rates and motorcycle crash fatality risk for the 12 months before and after the April 13, 2012, repeal with a statewide police-reported crash data set. We linked police-reported crashes to injured riders in a statewide trauma registry. We compared head injury before and after the repeal. Regression examined the effect of helmet use on fatality and head injury risk. Results. Helmet use decreased in crash (93.2% vs 70.8%; P Conclusions. Michigan’s helmet law repeal resulted in a 24% to 27% helmet use decline among riders in crashes and a 14% increase in head injury.