In 1987, New Zealand introduced a comprehensive Graduated Driver Licensing System (GDLS) which was designed to allow new drivers to gain driving experience while being excluded from high risk situations. This study sought to evaluate the impact of the GDLS on motorcycle traffic crashes that resulted in serious injury. Injury crash data were obtained from the New Zealand Health Information Services national public hospital inpatient data files for the years 1978-1994, inclusive. Cases were disaggregated into three age groups, 15-19 years, 20-24 years, and 25 years or older, for which injury trends were obtained. In order to determine whether trends in motorcycle traffic crashes simply followed national trends in other injury events, two non-traffic comparison groups for the main target group (15-19 years) were included. Using time series analyses, the introduction of the GDLS was found to be closely followed by a significant reduction (22%) in motorcycle traffic crash hospitalizations for the 15-19 year age group. An examination of vehicle registration and driver licensure data suggests that the reduction in injury crashes may, largely, be attributable to an overall reduction in exposure to motorcycle riding.