PURPOSE: Environmental factors modulate oral-health-related quality of life (OHRQoL). The aim of this study was to analyse sociodemographic and behavioural factors affecting the OHRQoL in Spanish adolescents, by using the Child-OIDP (Child-Oral Impacts on Daily Performances) index. MATERIALS AND METHODS: A cross-sectional study was conducted in 337 adolescent schoolchildren aged 13-15 years. A questionnaire on sociodemographic, behavioural and oral self-perception factors was administered with the Child-OIDP questionnaire. Descriptive statistics, Kruskal-Wallis and Mann-Whitney U-tests, as well as a regression model were used in the data analysis. RESULTS: The overall mean Child-OIDP index was 3.28±6.55. It was statistically significantly higher in females than in males (p < 0.001). Mothers having a managerial job showed statistical association with worse OHRQoL (p < 0.001). Caries experience and history of dental trauma were not associated with the oral-health-related quality of life (p > 0.05). Halitosis statistically significantly affected the activities of daily living (p < 0.001). Perceived dental problems, dental treatment needs, self-assessment of oral health status and satisfaction with oral health were associated with the impact index (p < 0.05). CONCLUSION: Mothers who were managers, female sex, presence of halitosis, and perceived dental treatment needs were the most important predictors of the impact index, while dietary habits, oral hygiene, and dental visits did not affect it. Knowledge of these factors will help dental professionals to apply adequate preventive and therapeutic measures.