Aims and objectives. To understand (1) the change of stage of changes, self-efficacy, decisional balance and processes of change for sexual abstinence behaviour across a 15-month interval, (2) relations of baseline stage of changes, self-efficacy, decisional balance and processes of change to follow-up stage of changes for sexual abstinence and (3) the important predictors of follow-up stage of changes and transition of stage of changes for sexual abstinence behaviour.Background. Examining factors of sexual abstinence behaviour among adolescents can provide useful information in designing sexual abstinence intervention programmes.Design. This study applied a transtheoretical model and used a longitudinal design.Method. Anonymous questionnaires were administered to 281 participants at baseline and 15-month follow-up.Results. In summary, 46·3% (n = 130) of the participants were in the same stage, 30·2% (n = 85) regressed and 23·5% (n = 66) progressed their stage from baseline to follow-up. Baseline self-efficacy, decisional balance and processes of change are related to follow-up stage of changes for sexual abstinence. Participants with higher baseline self-efficacy, lower decrease of self-efficacy from baseline to follow-up and lower decrease of decisional balance from baseline to follow-up were more in the definite group (preparation and action stage) at follow-up. Participants with higher baseline decisional balance, lower decrease of decisional balance from baseline to follow-up and lower decrease of self-efficacy from baseline to follow-up were more in the advancement transition group at follow-up.Conclusions. Focus of interventions could differ according to intervention purpose. Reducing the decrease of self-efficacy and decisional balance across time is important to enable adolescents to be in or progress to better stages across time.Relevance to clinical practice. To make adolescents be in later stages at follow-up, increasing baseline self-efficacy is important. If the purpose is to progress the stages, baseline decisional balance should be emphasised. Health care providers should continually boost the self-efficacy and decisional balance of adolescents across time.