The folk high school (FHS) is a Nordic contribution to global education and is a unique approach to non-university adult education. Because expanded tuition is the true nature of Norwegian FHS, it is important for FHS that its teachers perform discretionary individual extra-role behaviour advantageous to the school organization, a phenomenon called organizational citizenship behaviour (OCB). The purpose of this article is to explore the antecedents of organizational citizenship behaviour among teachers at Norwegian FHS and examine the relative impact of these aspects on OCB. The study is rooted in an integration of two strands of theories that have their focal point on employees' perceptions of exchange: (1) Shore's theory on employee-organization relationships and (2) Bryk and Schneider's theory on trust in schools. We tested a structural model using cross-sectional data. A questionnaire was distributed to all teachers at Norwegian folk high schools, which resulted in data from 366 teachers, representing a response rate at teacher level of 56%. The research strongly supports the importance of good relations between teachers and school leaders for OCB. The study also indicates that teacher commitment is an important mediating variable between relational trust between leader and teachers and OCB. (Contains 1 table and 2 figures.)