Using cross-sectional time series data for the 50 states and Washington, DC, covering the period 1975-2004, we estimate fixed effects regression models that examine the effects of universal and partial helmet laws on three different motorcyclist fatality rates, while controlling for other state policies and characteristics. Depending on the particular measure that is employed, states with universal helmet laws have motorcyclist fatality rates that are on average 22-33% lower in comparison to the experience with no helmet law. Additionally, partial coverage helmet laws are associated with reductions in motorcyclist fatality rates of 7-10%, on average.