To examine the impact of later trading hours for licensed hotels (Australian public houses are usually known as "hotels") in Perth, Western Australia, on levels of violent assault on or near these premises. Data on assault offenses reported to police between July 1, 1991, and June 30, 1997, were examined to identify those offenses that occurred on or close to hotels. During this period, 45 (24%) of the 188 hotels meeting study criteria were granted an extended trading permit for 1AM closing ("ETP hotels"), whereas the rest continued to close at midnight ("non-ETP hotels"). A time-series analysis employing linear regression was used to test whether there was a relationship between the introduction of extended trading and monthly rates of assaults associated with ETP hotels, while controlling for the general trend in assault rates among normally trading hotels. Possible confounders and other variables of interest (e.g., levels of alcohol purchases) were also examined. After controlling for the general trend in assaults occurring throughout Perth hotels, there was a significant increase in monthly assault rates for hotels with late trading following the introduction of extended trading permits. This relationship was largely accounted for by higher volumes of high alcohol content beer, wine and distilled spirits purchased by late trading hotels. Late trading was associated with both increased violence in and around Perth hotels and increased levels of alcohol consumption during the study period. It is suggested that greater numbers of patrons and increased levels of intoxication contributed to the observed increase in violence and that systematic planning and evaluation of late trading licenses is required.