A comprehensive study was conducted in Maryland of all motorcycle traffic crashes occurring during a 1-year period. All available medical and cost data were linked with police crash reports. During the study period, 1900 motorcycle drivers were involved in crashes. The data indicated that 1) helmet usage was 35% overall, 30% among fatally injured drivers, and only 16% among drivers with a history of drug/alcohol conviction, 2) unhelmeted drivers seen at an emergency department were almost twice as likely to have sustained head injury (40%) as were helmeted drivers (21%) (the corresponding percentages for hospitalized drivers were 55% and 38%), and 3) acute care cost for unhelmeted drivers was three times ($30,365) that of helmeted drivers. (This research was supported, in part, by a grant from the National Highway Traffic Safety Administration, U.S. Department of Transportation, and the Maryland Department of Transportation.)