Although the oral health among young adults in Sweden is generally good, there are groups where poor oral health remains a problem. The aim of this thesis is to increase our knowledge of oral health and oral health-related behaviors among young adults with caries disease, and to evaluate the ability of a brief form of Acceptance and Commitment Therapy (ACT) to promote oral health and oral health behaviors in this group of individuals at the Public Dental Service Clinics. The studies included are based on a randomized controlled trial carried out in a sample of 18-25-year-olds, with ≥ 2 new approximal dentin caries lesions since their last dental examination. In Study I, we analyzed baseline data to describe oral health, oral health-related quality of life (OHRQoL), oral health behaviors, and the association between different known risk factors for poor oral health and caries severity. The results demonstrate that, in general, the young adults suffered from poor oral health, negatively affected OHRQoL, and they engaged in different oral health risk behaviors. Levels of gingivitis, the frequency of sugary soda consumption, poor OHRQoL and less frequent dental attendance were found to be associated with the caries severity. Study II evaluated the direct effect of ACT on oral health behavior, and Study III evaluated the effect on the levels of gingivitis and plaque at the 9-week and 18-week follow-ups. Study II showed a promising direct effect of ACT on oral hygiene behaviors, in favor of ACT treatment. In Study III, reduced gingivitis and plaque levels were found both in the intervention and the control group. Although slightly lower levels of plaque and gingivitis were maintained in the intervention group at the 18-week follow-up, the improvement was not statistically significantly better than in the control group. The finding in Study I emphasizes the need to develop effective interventions to promote oral health in this subgroup of young adults. Study II and III contribute with important knowledge but also acknowledge the need for further development and evaluation of theory-based interventions in the dental field.