Objetivos: O transtorno de déficit de atenção/hiperatividade (TDAH) é um transtorno mental com alta prevalência em crianças e adolescentes, causando prejuízos importantes no funcionamento dos indivíduos acometidos. A presente revisão visa a orientar o psiquiatra sobre alguns dilemas clínicos e terapêuticos freqüentemente encontrados no tratamento desses pacientes. Métodos: Revisão abrangente, não sistemática da literatura sobre as seguintes questões: a) diferenciação normalidade/presença do transtorno; b) importância clínica do critério de idade de início de prejuízo dos sintomas; c) a fronteira com quadros de transtorno de humor bipolar (THB); d) diretrizes terapêuticas na presença de comorbidades. Resultados: São apresentadas dicas clínicas para caracterizar o diagnóstico sem aumentar significativamente a proporção de falsos positivos no grupo dos portadores do transtorno, bem como para auxiliar tanto no diagnóstico diferencial com THB quanto no manejo farmacológico do transtorno na presença de comorbidades. Con-

lthough it is widely accepted that attention-deficit/ hyperactivity disorder (ADHD) often begins in Objective: Since DSM-IV criteria for attention-deficit/hyperactivity disorder (ADHD) require that some symptoms causing impairment must be present before 7 years of age, clinicians are faced with a diagnostic and treatment dilemma on how to proceed with late-onset ADHD patients. We aimed to compare the response to methylphenidate between a group of patients fulfilling all DSM-IV ADHD criteria (full ADHD diagnosis) and a group of patients fulfilling all DSM-IV criteria except the age-atonset criterion (late-onset ADHD). Method: We evaluated 180 children and adolescents (4-17 years old) and 111 adults from our ADHD unit. All ADHD diagnoses were assessed using DSM-IV criteria. Methylphenidate was administered twice daily (8 a.m. and noon), but an extra dose was allowed between 5 and 6 p.m. for children and adolescents needing extra coverage in the evening. The minimum dose was 0.30 mg/kg/day. Response to treatment was assessed in methylphenidate-naive subjects using the Swanson, Nolan, and Pelham Scale-version IV (SNAP-IV) at baseline and after 1 month of treatment. Data were collected from January 2000 to January 2006. Results: In both samples, subjects with the full ADHD diagnosis did not have a better response to methylphenidate at doses around 0.5 mg/kg/day than the late-onset ADHD subjects. In fact, adults with late-onset ADHD had a better response to methylphenidate than adults with the full diagnosis, even after adjustment for confounders (baseline SNAP-IV total score and ADHD types) (children and adolescents: F = 0.865, p = .354; adults: F = 5.760, p = .018). Conclusion: These results concur with recent literature questioning the validity of the DSM-IV age-at-onset criterion for the diagnosis of ADHD and suggest that clinicians should consider implementing methylphenidate treatment for subjects with late-onset ADHD.