Objective We explored parents' accounts of the parent‐clinician relationship in childhood cancer to understand how parents who perceive threats to the relationship can be supported. Methods Multicentre longitudinal qualitative study, with 67 UK parents of children (aged 1‐12 years) receiving treatment for acute lymphoblastic leukaemia. Analyses drew on the wider sample but focussed on 50 semistructured interviews with 20 parents and were informed by constant comparison. Results All 20 parents described problems with clinical care such as inadequate information or mistakes by staff but varied in how much the problems threatened their sense of relationship with clinicians. Some parents saw the problems as having no relevance to the parent‐clinician relationship. Others saw the problems as threats to the clinical relationship but worked to “contain” the threat in ways that preserved a trusting relationship with at least one senior clinician. Parents' containment work protected the security they needed from the parent‐clinician relationship, but containment was a tenuous process for some. A few parents were unable to contain the problems at all; lacking trust in clinicians, these parents suffered considerably. Conclusions Given the complexity of childhood cancer care, problems with clinical care are inevitable. By engaging in containment work, parents met their needs to feel secure in the face of these problems, but the extent to which parents should have to do this work is debatable. Parents could benefit from support to seek help when problems arise which threaten their trust in clinicians. Attachment theory can guide clinicians in giving this support.