this transversal study aims to identify vulnerability experienced by adolescents of public secondary schools in cuiabá, mato grosso, brazil. the results show that 10.5% of the boys and 5.8% of the girls have already used illicit drugs - at the age of 15, cocaine (28.9%) and marijuana (15.7%) being the most reported; 45.2% of the boys and 52.4% of the girls consume alcoholic beverages, being beer the most common. among those who declared to be smoker (16.0%), the majority began smoking at the age of 15. sexual violence was reported, out of which only 33.3% of the boys and 25.0% of the girls sought help. among those who did not seek help, the referred motive was fear and shame. the need for specific prevention and treatment services for adolescents in vulnerable situations is stressed, in view of the occurrence and consequences of this kind of harm.