Dropout of treatment is one of the key issues in outcome in a child and adolescent mental health service. We report two studies focusing on the treatment process and the dropout rate of children with persistent conduct problems presenting to a community mental health service, using a prospective design. The first study included 32 children and used a randomised controlled treatment design comparing a CBT approach with conjoint family therapy and an eclectic approach. The overall dropout rate was 36%. Dropout occurred significantly less frequently in the CBT group. The dropout group was associated with mothers who were younger and less educated, a poorer rating by the clinicians at the last meeting, parental dissatisfaction with the treatment service and perception that the treatment was less organised and having less behavioural tasks. In the second study we used a naturalistic follow-up design. Forty-six children were included. The overall dropout rate was 48%. Again, the children who defaulted were rated by clinicians as less likely to have improved and dropout was also significantly associated with parental perception of a less organised treatment. In both studies dropout usually occurred after assessment and at the early phase of treatment.