The aim of this study was evaluate the effect of a Swedish educational programme encouraging the use of bicycle helmets. Another to important aim was to use a theoretical model to explain which factors contribute to the prediction of cyclists' intention to use a helmet. A non-representative sample consisting of employees working for the same insurance company located at three different locations in Sweden was selected. Two served as an experiment group and the third as a control or comparison group. Measurements were taken before and after the campaign. The educational campaign was held by the Swedish Falck Ambulans. The session lasted for one hour. The emphasis of the campaign was to focus on accidents and injuries to the brain when not wearing a helmet. The participants were also given an opportunity to sign a bicycle helmet contract on receipt of which they received a helmet free of charge. Data were collected using a web-based self-report survey. The results revealed that the proportion of people who used a helmet when biking to work had increased substantially amongst those having taken part in the session. It also showed that after the campaign the intention to use the helmet was greater amongst the experiment group than amongst the control group. The results showed that the Theory of Planned Behaviour (TPB) was effective in the predicting of the intention to wear a helmet. The strongest predictor was perceived behavioural control followed by subjective norm. The weakest TPB predictor was the attitude. The prediction of helmet wearing intention was significantly improved when anticipated regret and past behaviour were added to the model. The results from the Transtheoretical model showed that participants in the experimental group had on average moved one step closer to a change. In sum, it could be concluded that an educational campaign, which also includes elements of endorsement (i.e. to be given a bicycle helmet when signing a contract to use the same), significantly increases the likelihood of using a bicycle helmet.