Objective: To define the prevalence of attention-deficit/hyperactivity disorder (ADHD) in children from four Brazilian public elementary schools. Method: Study population consisted of all students from the first through fourth grades, age range 6-12 years, who attended four public elementary schools (CIEPs). This prevalence study comprised two steps. During the first step, school teachers screened their own pupils for ADHD using diagnostic criteria from the Diagnostic and Statistic Manual of Mental Disorders - Fourth Edition (DSM-IV). Screening resulted in two groups of children: suspects and non-suspects. In the second step, parents of suspect children were invited for an interview with the researchers, during which they filled ADHD symptoms questionnaire, and in addition a complete history, pediatric physical exam, and neurological exam were performed. At the end of this step, students were classified as "cases" or "undetermined", i.e., those who partially met ADHD diagnostic criteria. Results: From a population of 602 students, 461 were recruited. Considering all four elementary schools, ADHD prevalence was 13%. Male to female ratio was 2:1. The most frequent ADHD subtype was the combined one, accounting for 61.7% of all cases. Conclusion: ADHD prevalence in a sample of school-aged children (13%) was higher than the rate that traditionally has been mentioned (3-5%). Boys were more frequently affected than girls and the most prevalent ADHD subtype was the combined subtype, and the latter two findings are concordant with previous studies.651134137Clinical practice guideline: Diagnosis and evaluation of the child with attention-deficit/hyperactivity disorder (2000) Pediatrics, 105, pp. 1158-1170. , American Academy of PediatricsReiff, M.I., Stein, M.T., Attention-deficit/hyperactivity disorder evaluation and diagnosis: A practical approach in office practice (2003) Pediatr Clin N Am, 50, pp. 1019-1048McGough, J.J., McCracken, J.T., Assessment of attention-deficit/ hyperactivity disorder: A review of recent literature (2000) Curr Opin Pediatr, 12, pp. 319-324Rodhe, L.A., Busnello, E.A., Chachamovitch, E., Vieira, G.M., Pinzon, V., Ketzer, C.R., Transtorno de déficit de atenção/hiperatividade: Revisando conhecimentos (1998) Revista ABP-APAL, 20, pp. 166-178Associação Americana de Psiquiatria. Transtornos geralmente diagnosticados pela primeira vez na infância ou na adolescência. In Manual diagnóstico e estatístico de transtornos mentais, 4. a edição. Porto Alegre: Artes Médicas Sul2000: 37-119Cantwell, D.P., Baker, L., Attention-deficit disorder with and without hyperactivity: A review and comparison of matched groups (1992) J Am Acad Child Adolesc Psychiatry, 31, pp. 432-438Baumgaertel, A., Wolraich, M.L., Dietrich, M., Comparison of diagnostic criteria for attention deficit disorders in a German elementary school sample (1995) J Am Acad Child Adolesc Psychiatry, 34, pp. 629-638Steinhausen, H.C., Drechsler, R., Földényi, M., Imho, K., Brandeis, D., Clinical course of attention-deficit/hyperactivity disorder from childhood toward early adolescence (2003) J Am Acad Child Adolesc Psychiatry, 42, pp. 1085-1092Vasconcelos, M.M., Werner Jr, J., Malheiros, A.F.A., Lima, D.F.N., Santos, I.S.S.O., Barbosa, J.B., Prevalência do transtorno de déficit de atenção/hiperatividade numa escola pública primária (2003) Arq Neuropsiquiatr, 61, pp. 67-73Newcorn, J.H., Halperin, J.M., Schwartz, S., Parent and tearcher ratings of attention-deficit hyperactivity disorder symptoms: Implications for case identification (1994) J Dev Behav Pediatr, 15, pp. 86-91Vasconcelos, M.M., Malheiros, A.F.A., Werner Jr., J., Contribuiç ão dos fatores de risco psicossociais para o transtorno de déficit de atenção/ hiperatividade (2005) Arq Neuropsiquiatr, 63, pp. 68-74Dunn, D.W., Kronenberger, W.G., Attention-deficit/hyperactivity disorder in children and adolescents (2003) Neurol Clin, 21, pp. 933-940Rohde, L.A., ADHD in Brazil: The DSM-IV criteria in a culturally different population (2002) J Am Acad Child Adolesc Psychiatry, 41, pp. 1131-1133Mitsis, E.M., McKay, K.E., Schultz, K.P., Newcorn, J.H., Halperin, J.M., Parentteatcher concordance for DSM-IV attention-deficit/hyperactivity disorder in a clinic-referred sample (2000) J Am Acad Child Adolesc Psychiatry, 39, pp. 308-313Schachar, R., Rutter, M., Smith, A., The characteristics of situationally and pervasively hyperactive children: Implications for syndrome definition (1981) J Child Psychol Psychiatry, 22, pp. 375-392Rapoport, J.L., Donnelly, M., Zametkin, A., Carrougher, J., Situational hyperactivity in a US clinical setting (1986) J Child Psychol Psychiatry, 27, pp. 639-646