Background To study the cross‐informant agreement between father, mother harm avoidance and child rating of health‐related quality of life (HRQoL) in a psychiatric sample. Methods Data were obtained from 127 children and adolescents (aged 6–18) commencing outpatient psychotherapy treatment, mainly for anxiety, depressive, and externalising disorders. A total of 100 mothers, 69 fathers harm avoidance and 76 children (aged 11 years and older) filled out questionnaires. HRQoL was measured with the KIDSCREEN‐27. Results Cross‐informant agreement was moderate to high between parents and moderate to low between father–child and mother–child pairs. Both parents reported lower HRQoL than the children themselves. Standardised discrepancies correlated with gender, overall and internalising pathology, as well as harm avoidance to a small degree. Conclusions Although there was moderate‐to‐high correspondence, mother and father reports were not interchangeable. When collecting a single‐parent proxy rating on the child's HRQoL, researchers should be aware of the additional potential source of variance due to differing concordance of father and mother with the child's self‐report especially for peer relations.