Objective This study examined the relationships between parental posttraumatic stress symptoms (PTSS), child PTSS, and parent–child concordance for child PTSS. Method Participants were children with cancer (n = 199), and healthy children (n = 108) and their parents. Children self‐reported on PTSS and parents completed measures of child and parent PTSS. Results In the cancer group, child and parent reports of child PTSS were significantly correlated with no mean differences between reporters. In contrast, correlations were non‐significant in the control group, and parents reported significantly lower levels of child PTSS than children. Increased parental PTSS was associated with better concordance in the cancer group but not in the control group. In fact, in the cancer group, parent–child concordance was strongest at the highest level of parental PTSS. Conclusions Parents of children with cancer were found to be accurate reporters of their children's distress, even with high levels of reported personal distress. In contrast, parents of healthy children appear primarily influenced by personal distress when reporting child PTSS. Although multiple informant assessments are always desirable, it appears that utilization of a single informant may be reasonable in the cancer setting when access to informants is limited. Copyright © 2013 John Wiley & Sons, Ltd.