Multi-informant diagnosis is regarded as best practice in child clinical assessment. However, parents and children typically provide dissimilar information, exhibiting low cross-informant agreement; such has serious implications for assessment and treatment. The current study examined the level of agreement between parent- and child- reported child posttraumatic stress disorder (PTSD) in children admitted to pediatric intensive care units (PICUs). The influences of child age, child gender and parental distress on the level of agreement were also explored. 73 children, aged 6-16, and their parents were recruited from two hospitals in Queensland, Australia. Parents and children completed questionnaires assessing PTSD symptoms 3 months following discharge from PICU. Overall agreement between parents’ and their children’s reports of child PTSD were moderate (r = .49; κ = .38). No significant differences in levels of cross-informant agreement were found between school-aged children and adolescents, and between girls and boys. In contrast, although differences in informant agreement between PTSD-positive and PTSD-negative parents did not reach statistical significance, there was considerable discrepancy between reports of PTSD-positive parents and their children. Moreover, parents with elevated distress tended to rate their children more severely; this is likely due to the influence of parental PTSD symptoms, which contributed significant variance to parents’ ratings of child PTSD symptoms, even after controlling for child self-reported distress. Overall findings highlight that child and parent reports are not interchangeable and should be incorporated to achieve a comprehensive assessment of child functioning. The results suggest that since psychopathological parents might be negatively biased in their evaluations of child behaviour, clinicians should assess parents’ symptom statuses and exercise caution when interpreting reports from pathological parents, especially in cases of discordant responses.