Background: It appears that many commercial alcohol outlets fail to comply with minimum age laws. This means that alcohol is readily available, from a variety of different types of outlets, to underage adolescents who wish to purchase it.Objectives: The aims of this study were to assess the ease with which adolescents in the United Kingdom are able to buy alcohol, to obtain information concerning vendors perceptions of alcohol sales to adolescents, and to evaluate a police intervention intended to reduce underage alcohol sales.Main characteristics: An unobtrusive naturalistic field study was conducted in two urban locations.Evaluation: Overall, there was no evidence that the police intervention reduced sales of alcohol to 16-year-olds. There was a hint that the intervention may have caused a very short-lasting decrease in sales to 13-year-old girls, but this was contained within an overall increase in sales to this group. Alcohol vendors reported that they rarely encountered underage customers or refused sale, although 90% of vendors said that if they became suspicious, they would request ID.Conclusion: These data suggest that 16-year-olds, and girls as young as 13, have little difficulty in purchasing alcohol, and that there is little difference between different types of outlets in their willingness to sell alcohol to minors. The fact that the police intervention failed to decrease sales suggests that vendors do not change their behaviour in response to the threat of legal action.