BACKGROUND: Teenagers and young adults are more exposed to violence and traumatic events than adults, and these factors can be associated with mental disorders. This paper aims at investigating whether young people are more exposed to violence and traumatic events and to compare pattern of mental disorders with adults. METHODS: Cross-sectional study using the Composite International Diagnostic Interview, conducted between 2007 and 2008 with a randomly selected sample of 15 to 75 year-old residents of São Paulo, Brazil. RESULTS: Two thousand five hundred thirty-six participants were divided into two groups: 1096 (43.2 %) young people (15 to 24 years), and 1440 (56.8 %) adults (25 to 75 years). 12-month exposure to traumatic events was higher among young people (32.1 % vs. 20.6 %; p < 0.001). Assaultive violence was reported by 13.4 % of young people and 8.6 % of adults (p = 0.012); 20.1 % of young people and 13 % of adults reported suffering other injury or shocking events (p < 0.001); sudden death/life threatening illness of a close person was declared by 6.1 % of young people and 3.2 % of adults (p = 0.017). Prevalence of alcohol related disorders was higher among young people (5.4 % vs. 2.5 %; P = 0.032); depressive disorders were more prevalent among adults (9.0 % vs. 4.7 %; P = 0.004). Alcohol related disorders were associated to assaultive violence among young people (OR = 3.4; 95 % CI = 1.36 to 8.52; p = 0.004) and adults (OR = 2.38; 95 % CI = 1.23 to 4.61; p = 0.002). Phobic/anxiety disorders were associated to other injury or shocking events among young people (OR = 1.28; 95 % CI = 0.67 to 2.44; p = 0.025). Major depressive disorder was associated to assaultive violence among young people (OR = 2.27; 95 % CI = 1.09 to 4.74; p = 0.004) and adults (OR = 1.28; 95 % CI = 0.85 to 1.93; p = 0.009). CONCLUSION: Exposure to violence and traumatic events was higher among young people. Alcohol related disorders, depression and phobic/anxiety disorders were significantly higher among young people exposed to traumatic events. Despite the study design, high exposure to violence and traumatic events in this age group can be considered important factors in triggering mental disorders in this vulnerable age period.