Aim: Research shows there are associations between bar environments and alcohol-related harms. However, few European studies have examined such links. Our study investigates the type of harms experienced by patrons in European bars, and their relationships with individual, social and environmental factors. Design: Unobtrusive one-hour observational visits. Characteristics of the bar environment, staff and patrons, and harms observed were recorded on structured schedules. Setting: Bars in four cities in the Netherlands, Slovenia, Spain and the United Kingdom (U.K.). Participants: 238 observations across 60 bars. Measures: Analyses utilized chi-squared, analyses of variance and logistic regression. Findings: 114 incidents of harm were observed; in one-fifth of visits, at least one incident was recorded. People falling over, arguing or being so severely intoxicated that they required assistance to walk were the most common incidents observed. Bivariate analyses showed associations between a range of staffing, customer and environmental characteristics, and incidents of harm. Controlling for city and venue, only a permissive environment remained significant in multivariate analyses. Conclusions: Harms occurring in nightlife venues are typically minor. However, such incidents have the potential to escalate into more serious harms; thus, prevention is crucial. Prevention should focus on improving venue management practice and on the behavioral standards expected of customers.