Résumé : Background. In children and adolescents non-compliance with treatment is a major concern. To shed light on its mechanisms, we present a family demonstrating non-compliance. Procedure. B, a 10 year-old boy, treated for medulloblastoma, refused high-dose chemotherapy and Autologous Bone Marrow Transplantation. Six psychotherapeutic interviews with B, his parents and staff resolved the causative issues. Results. B's behavior expressed his parents' ambivalence, despite their informed consent. Their reasons were conscious and unconscious, rational and irrational, linked to both the past and present experiences. The mother was convinced that he would die. The discussions helped both parents to assume their parental role, B perceived their ability to truly accept the treatment and support him. Conclusions. Non-compliance should not be viewed as a child's or parents' intrapsychic problem, but as the result of multi-determined interaction between the child, the parents, the staff interacting with present and past events. When the child's death is a possibility, the parents' ambivalence confuses their understanding and acceptation of the therapy. The development of confidence between the staff, the child and parents and clear agreement about the goals of therapy is necessary to avoid the occurrence of and escalation of non-compliance, which raises difficult clinical, legal and ethical questions.