Purpose: The purpose of this paper is to provide insight into teachers' practice in implementing school-based health promotion. Design/methodology/approach: This qualitative research was designed as a multiple case study. The study involved five schools, 233 pupils in the age 12-16 and 23 teachers. The primary data generation method were focus groups. Findings: According to the national guidelines the health education in primary schools in Denmark should be based on the critical approach to health education developed within the European Network of Health Promoting Schools. However, the study showed that teachers' implementation of the guidelines in practice was closer to traditional health education, which focuses only lifestyle change, than to critical health education which also explores the underlying conditions for health. Research limitations/implications: The study explored teachers' implementation practices, and the individual and institutional factors that influence the practice. This paper restricts itself to examining teachers' practice against the national curriculum guidelines. Practical implications: The teachers were not sufficiently familiar with the curriculum guidelines or the critical approach to health education. The inclusion of the national curriculum and the principles of critical health education in the initial and in-service professional development of teachers is an urgent priority if this gap is to be reduced. Originality/value: This paper contributes to the debate related to the potentials and barriers for implementing of health promotion interventions in a school context.