OBJECTIVE To assess the immediate impact of the introduction of minimum unit pricing in Scotland on household alcohol purchases. DESIGN Controlled interrupted time series analysis. SETTING Purchase data from Kantar Worldpanel's household shopping panel for 2015-18. PARTICIPANTS 5325 Scottish households, 54807 English households as controls, and 10040 households in northern England to control for potential cross border effects. INTERVENTIONS Introduction of a minimum price of 50p ((sic)0.55; $0.61) per UK unit (6.25p per gram) for the sale of alcohol in Scotland on 1 May 2018. MAIN OUTCOME MEASURES Price per gram of alcohol, number of grams of alcohol purchased from off-trade by households, and weekly household expenditure on alcohol. RESULTS The introduction of minimum unit pricing in Scotland was associated with an increase in purchase price of 0.64p per gram of alcohol (95% confidence interval 0.54 to 0.75), a reduction in weekly purchases of 9.5 g of alcohol per adult per household (5.1 to 13.9), and a non-significant increase in weekly expenditure on alcohol per household of 61p (-5 to 127). The increase in purchase price was higher in lower income households and in households that purchased the largest amount of alcohol. The reduction in purchased grams of alcohol was greater in lower income households and only occurred in the top fifth of households by income that purchased the greatest amount of alcohol, where the reduction was 15 g of alcohol per week (6 to 24). Changes in weekly expenditure were not systematically related to household income but increased with increasing household purchases. CONCLUSIONS In terms of immediate impact, the introduction of minimum unit pricing appears to have been successful in reducing the amount of alcohol purchased by households in Scotland. The action was targeted, in that reductions of purchased alcohol only occurred in the households that bought the most alcohol.