Results indicated that exposure and sensitivity to most social and family risk factors for DBDs were equal among boys and girls. On the other hand, boys were more likely to experience neurodevelopmental problems, attention-deficit/hyperactivity disorder, and peer problems while exhibiting lower rates of prosocial behaviors than girls. These factors, combined with the greater likelihood of physical punishment for boys, may account for 54 percent of the observed sex differences in DBDs. At the 3-year follow-up, girls and boys with DBDs were similar with one exception: of those children exhibiting subthreshold conduct problems at initial assessment, boys were more likely than girls to develop DBDs at follow-up. Participants were 5,913 5- to 10-year-olds who completed the British Child and Adolescent Mental Health Survey in 1999 and 1,440 8- to 13-year-olds selected from the original sample for the 3-year follow-up assessment. Children in both the initial and follow-up assessments were given a DSM-IV diagnosis using the Developmental and Well-Being Assessment. Clinical implications of the findings are discussed and include the need for effective DBD interventions for young girls who display high levels of disruptive behaviors. Tables, references