Introduction: Deteriorating oral health is an emerging public health concern in developing countries, yet little attention has been given to oral health in most sub-Saharan countries. The extents of caries, periodontal diseases and the associated risk factors have not been widely studied at the community level. Purpose: To assess the type and magnitude of oral health diseases as well as associated risk factors among young adolescents in Addis Ababa, Ethiopia. Methods: A community-based cross-sectional study was conducted on a sample of 658 children aged 10 - 14 years in Addis Ababa. Households for the study were selected through a multistage cluster sampling procedure. Data collection was carried out in December 2011 through interview and oral examination which was carried out by dental health professionals. Prevalence and 95% confidence interval was calculated. Factors associated with oral health conditions were identified using logistic regression. Results: The prevalence of dental caries was 47.4% (95% CI: 43.6% - 51.2%). Age, sweets intake, tooth cleaning, poor oral hygiene and being from a poor household were significantly associated with having dental caries. The prevalence of periodontal disease was 35.4% (95% CI: 31.7% - 39.0%) and it was associated with: having a mother with low education level, and poor oral hygiene. The prevalence of bad mouth odor was 4.4% (95% CI: 2.8% - 5.9%), and oral trauma 2.1% (95% CI: 1% - 3.2%). Conclusion: The prevalence of both periodontal disease and dental caries is alarmingly high. The findings indicate the need for large scale public education program to motivate regular dental check up, and proper oral hygiene practices. The study also indicates the need to strengthen oral health services using affordable and accessible outlets.