To identify the prevalence and risk indicators of periodontal disease in high-school students in Tehran, Islamic Republic of Iran, the periodontal condition of 867 students aged 15–19 years was assessed using the community periodontal index of treatment needs (CPITN). The results showed that 88.7% of these students had less than perfect periodontal health. Multiple regression analysis revealed that sex, parents’ educational level, frequency of toothbrushing and flossing, preventive dental visits and presence of extracted teeth were significant risk indicators for periodontal disease. School-based oral health promotion and prevention programmes are needed.