OBJECTIVE: The objective of this study was to assess the impact of Saturday opening of alcohol retail shops in Sweden. METHOD: An experimental design was applied. Prior to February 2000, all alcohol monopoly outlets we closed on Saturdays. After this date, stores in an experimental area (six counties) were open on Saturdays. In the control area (seven counties) the shops remained closed. To prevent biases resulting from border trade, the experimental and control areas were separated by a border area (seven counties). The outcome measures included alcohol sales and indicators of assaults and drunken driving. The pre-intervention period covered January 1995-January 2000, and the post-intervention period February 2000-June 2001 (17 months). The data were analyzed on a monthly basis through ARIMA-modeling according to the Box-Jenkins technique. RESULTS: The analysis uncovered a statistically significant increase in alcohol sales of 3.3%. There were no significant changes in any of the assault indicators. There was a statistically significant increase in drunken driving (8.3%) on Saturdays-Sundays; however, further analyses suggested this increase was due mainly to a change in the surveillance strategy of the police. CONCLUSIONS: The Saturday opening of alcohol retail shops seems to have increased consumption but not alcohol-related harm. The absence of a significant effect on harm indicators could signify either that no such effect is present or that the design has insufficient power to uncover effects of the expected magnitude.