Objective Helmet use in Dutch recreational skiers and snowboarders (DRSS) remains low. This study evaluated the effects of exposure to a nationwide intervention on relevant determinants of helmet use and helmet use in DRSS. Methods The intervention mapping protocol was used to develop an in-season intervention programme targeted at adult DRSS. A prospective single-cohort study was conducted to evaluate the impact of intervention exposure on determinants of helmet use (ie, knowledge about head injury risk and preventive measures, risk perception, attitudes to head injury risk and helmet use and intention to helmet use) and self-reported helmet use. A random sample of 363 DRSS from an existing panel participated in this study. Data were collected using online questionnaires before and immediately after the 2010/2011 intervention season. In a separate sample of 363 DRSS, intervention reach was assessed after the 2010/2011 season. Results Overall, no significant associations were found between intervention exposure and the determinants of helmet use. However, subgroup analyses revealed intervention effects on risk perception and knowledge in specific subpopulations. Intervention exposure had a significant, positive effect on helmet use in DRSS (β=0.23; 95% CI 0.017 to 0.44). Subgroup analyses revealed that this effect was found in: (1) skiers, (2) female DRSS, (3) young skiers and (4) intermediate skiers. Overall, intervention reach was 28.1%, with differences found between skiers and snowboarders. Conclusions Exposure to a nationwide intervention programme was associated with increased self-reported helmet use in DRSS. Differences were found in intervention effectiveness and reach between subpopulations. These differences must be taken into account when developing and evaluating future interventions.