Aim This is an evaluation study of the impact of the adapted RCN Clinical Leadership Programme on the development of leadership competencies of nurse leaders in Switzerland.Background Transformational leadership competencies are essential for delivering high-quality care within health-care organizations. However, many countries have identified a lack of leadership skills in nurse leaders. Consequently, the development of leadership competencies is a major objective for health-care centres.Methods This article describes the quantitative results of a mixed methods study. A one-group pre-test–post-test quasi-experimental design was used. A convenience sample of 14 ward leaders were assessed three times using the Leadership Practices Inventory (LPI). Descriptive and inferential data analysis techniques were employed.Results In total 420 observer-assessment questionnaires and 42 self-assessment questionnaires were distributed. Our main finding was that nurse leaders following the programme, demonstrated significant improvement in two subscales of the LPI –‘inspiring a shared vision’ and ‘challenging the process’.Conclusion This study showed improvement in two leadership practices of nurse leaders following a programme that has been adapted to Swiss health care.Implications for nursing management Findings concur with others studies that suggest that investments in educational programs to facilitate leadership skills in nurse leaders are justified.