The aim of this systematic review and meta-analysis was to study the effectiveness of psychological interventions in adults and adolescents with poor oral health. The review follows the PRISMA guidelines for systematic reviews. The PICO format (population, intervention, comparison, and outcome) was used to define eligible studies. The populations were adults or adolescents (≥13 y of age and independent of others) with poor oral health (defined as dental caries, periodontal disease, and/or peri-implantitis). The interventions were psychological and/or behavioral models and theories, in comparison with traditional oral health education/information. The primary outcomes were dental caries, periodontitis, gingivitis, and peri-implantitis. Secondary outcomes were dental plaque, oral health-related behavior, health-related quality of life, health beliefs and attitudes, self-perceived oral health, and complications/risks. The systematic literature search identified 846 articles in December 2013 and 378 articles in July 2015. In total, 11 articles on 9 randomized controlled trials were found to meet the inclusion criteria. These reported on adults with periodontal disease, and several used motivational interviewing (MI) as their mode of intervention. The CONSORT guidelines and the GRADE approach were used for study appraisal and rating of evidence. The meta-analysis showed no statistically significant differences in gingivitis or plaque presence. In addition, a meta-analysis on MI compared with education/information found no statistically significant differences in gingivitis presence. Only 1 meta-analysis-on psychological interventions versus education/information regarding the plaque index-showed a small but statistically significant difference. There were also statistically significant differences reported in favor of psychological interventions in oral health behavior and self-efficacy in toothbrushing. However, the clinical relevance of these differences is difficult to estimate. The certainty of evidence was low. Future research needs to address several methodological issues and not only study adults with periodontal disease but also adolescents and patients with dental caries and peri-implantitis.