Daily dialogue between leaders and workers on traditional construction sites is primarily focused on production, quality and time issues, and rarely involves occupational safety and health (OSH) issues. A leadership training program entitled 'Toolbox-training' was developed to improve construction foremen's knowledge and communication skills in daily planning of work tasks and their related OSH risks on construction sites. The program builds on the popular 'toolbox meeting' concept, however there is very little research evaluating these types of meetings. This article describes the development, implementation and feasibility of the Toolbox-training program, and the results of the process evaluation and outcome evaluation. A total of 57 foremen from 12 companies participated in the training in five successive groups during 2014-2015. Following each group, the program was continuously evaluated and revised until the final version after the fifth group. The evaluation utilized an action research strategy with a mixed-methods approach of triangulating questionnaire, interview, and observation data. Process evaluation results showed that the eight Toolbox-training topics were relevant and useful for the majority of the foremen, who experienced positive changes in their daily work methods and interactions with their crews, colleagues, leaders, customers and other construction professions. The program is a unique contribution to leadership training in the construction industry, and can potentially be applied and adapted in many other sectors. However, there is still a need for testing the long-term effects of the program on safety climate, injuries and business in future studies.