In 1992, a package of measures was adopted by the city of Barcelona to obligate riders of motorcycles with a power capacity inferior to 125 cc to use helmets, until then only compulsory for larger motorcycles. Interrupted time series analyses with the use of a control group is used to investigate the effect of these measures on the number of serious injuries and number of deaths. The results indicate a significant decrease in the number of serious cases in the treated group-smaller motorcycles and mopeds-a decrease which does not occur in the control group -larger motorcycles. The impact of the adopted measures is abrupt and permanent but the change in riders helmet wearing habits has not been influenced so much by the media campaign as by the coming into force of the legislation with the potential application of sanctions. © 1995.