Workplace health promotion programmes (WHPPs) are among the most important measures to improve the health and motivation of the ageing workforce. However, they are accompanied with certain challenges, such as low participation rates and higher participation levels of the more health-conscious workers, often failing to engage those who need such interventions the most. Following the PRISMA guidelines, this scoping review examined participation rates reported in articles on WHPPs to identify potential knowledge gaps. The results are worrying: participation rates are not only infrequently reported, but also low. Of the 58 articles, 37 report participation rates, with the majority (20) reporting an average participation rate of less than 50%. Reported participation rates refer either to different target groups, the type of intervention, or to single points in time, which makes it difficult to establish consistent criteria for comparison. We argue that despite the importance of WHPP efficacy, research focus should shift to the determinants of participation, as well as the issue of standardising the reporting of participation rates, alongside the potential problem of reporting bias.