Objectives: (1) For crashes on a public road, to compare serious cyclist crashes involving a motor vehicle with cyclist crashes not involving a motor vehicle, in terms of threat to life and length of stay in hospital. (2) To determine the proportion of all serious crashes involving cyclists on public roads which are recorded by the police. (3) To determine the degree to which under-reporting of serious crashes involving cyclists and motor vehicles on public roads is associated with various demographic, environmental, and injury factors. Study design: Records for the period 1995–99, of cyclists seriously injured on a public road and hospitalised were linked to the traffic crash report (TCR) database maintained by Land Transport Safety Authority (LTSA). Results: Of the 2925 cyclist crashes on public roads, only 652 (22%) could be linked to a TCR. Of the crashes involving motor vehicles (n = 1033), only 562 (54%) could be linked to the LTSA database. Age, ethnicity, injury severity, and cumulative length of stay were the only variables that predicted whether hospitalised cycle crash cases were more likely to have a corresponding TCR. There were substantial numbers of cyclist only crashes which typically are not captured in the TCR database. Nine percent of these resulted in serious or worse injury (that is, International Classification of Diseases/abbreviated injury scale score of 3+) and 7% resulted in hospital stays greater than seven days. Conclusion: Greater effort and precision needs to be applied to routinely document the burden of cyclist crashes, especially cyclist only crashes.