This study examined the prevalence, degree of association and differential effect, by sex and age, of conduct disorder symptoms on psychopathology and functioning. Participants included 680 Spanish children and adolescents between 8 and 17 years and their parents, attending to psychiatric outpatient consultation. Data were obtained through structured diagnostic interviews, and other measures of psychopathological outcomes and functional impairment. In general, the prevalence of antisocial behavior did not differ significantly by sex or age. Results indicated a higher frequency for 13-17 year olds, and a greater number of symptoms in boys. Moreover, some symptoms of conduct disorder showed developmental variations. Sex and age differentially affected the expression of some conduct disorder symptoms and their associations with functional impairment and severity of psychopathology. Knowing the different expression of each symptom could help to identify these problems in clinical children and adolescents, contributing to an early detection of population at the highest risk of serious psychopathology and worse prognosis.