INTRODUCTION The phenomenon of youth preloading with alcohol is related to increased rates of assault, injury and arrest. We have no empirical, field-based, research on the impact of preloading and alcohol use at a large-scale public event. METHOD Random samples of patrons were breathalysed (BrAC) on entry and exit of a horse racing/music event (n = 286), and questioned regarding their preloading, spending, and group characteristics. RESULTS 79% of participants sampled at entry and 85% at exit reported preloading prior to the event. Of those who preloaded, 87% were observed to have BrAC readings over zero (with a mean BrAC of .071 at a median time of day of 12.29 pm). No differences were found between genders on preloading or BrAC at entry. Group size was found to explain 9% of the unique variance in entry BrAC. Those patrons who preloaded had significantly higher BrAC at exit, with preloading accounting for almost identical variance to the number of reported drinks consumed within the venue. IMPLICATIONS Preloading at large-scale public events is highly endorsed by both male and female youth and is associated with a pattern of continued drinking throughout the course of the event. Interventions to manage risk are suggested.