Introduction: Different Brazilian and regional surveys detected a high prevalence of drugs use among children and adolescents, particularly among individuals under social risk conditions. Objective: This study aimed to determine the prevalence of drug use among institutionalized children and adolescents; to assess the degree of associated use of illicit drugs with alcohol and tobacco; and to determine which is the gateway drug to illicit drug use. Methods: A cross-sectional study was carried out in the Fundação Estadual do Bem Estar do Menor, in Porto Alegre (FEBEM) Southern Brazil. A questionnaire developed by the World Health Organization to determine prevalence off drug use was answered anonymously by a population of literate minors who were in FEBEM because of delinquency or due to social risk. The analysis aimed to describe the frequency of use of each drug and relate it to gender, age of beginning, and reason of institutionalization. Results: A total of 382 participants answered the questionnaire. The substances most frequently used on an experimental basis were: alcohol (81,3%), tobacco (76,8%), marijuana (69,2%), cocaine (54,6%), inhalants (49,2%), anxiolytic drugs (13,4%), hallucinogens (8,4%), amphetamines (6,5%) and barbiturates (2,4%). Overall, around 80% of the respondents reported having used some illicit drug at least once in the past. Licit drugs, like alcohol and tobacco, were used mainly by males, while medicines were used mostly by females. Adolescents with delinquency records showed a significantly higher frequency of alcohol, marijuana, cocaine, and solvent use. The mean age of beginning was under 12 years for alcohol and tobacco use, under 13 years for marijuana and inhalants, and under 14 years for cocaine. Concomitant use of illicit and licit drugs was found to be high in this population. Conclusions: A high prevalence of precocious drug use was found among institutionalized children and adolescent, with alcohol and tobacco being used earlier than illicit drugs. Delinquent males were more likely to have used illicit drugs.Adolescents. Licit and illicit drugs. Substance abuse.Objetivo: Identificar a prevalência do uso de drogas entre crianças e adolescentes institucionalizados e avaliar o uso associado das substâncias lícitas, álcool e tabaco, com drogas ilícitas e verificar qual a droga de uso inicial para o consumo das substâncias psicoativas ilícitas. Métodos: Realizou-se um estudo transversal na Fundação Estadual do Bem-Estar do Menor do Rio Grande do Sul, na cidade de Porto Alegre. Um questionário elaborado pela Organização Mundial da Saúde, anônimo, sobre o uso de drogas e sua quantificação, auto-aplicado em salas de aula, foi respondido pela população de crianças e adolescentes alfabetizados que cumpriam medidas sócio-educativas ou medidas protetivas. A análise visou descrever o uso de drogas entre os dois subgrupos levando em conta gêneros e idades de início de uso. Resultados: Os resultados foram obtidos a partir de 382 indivíduos. As substâncias mais experimentadas foram: álcool ...