Objective Screening for psychological distress is an important tool for improving survivors’ access to psychosocial care. The Brief Symptom Inventory-18 (BSI-18) has been widely used to identify psychological distress in cancer survivors, but few studies have reported on its validity. This study evaluated validity of the BSI-18 by comparing it to the Symptom Checklist-90 (SCL-90). Methods Concordance of cases identified by the BSI-18 and SCL-90 was examined in a sample of 193 adult survivors of childhood cancer. Results Receiver operating characteristics analysis showed strong diagnostic utility of the BSI-18 (area under curve = 0.922). However, the standard BSI-18 case-rule demonstrated low sensitivity (45.2%) against the SCL-90. An alternative case-rule showed better results; sensitivity (87.10%), specificity (83.33%). Conclusions The BSI-18 is a useful measure for evaluating distress in adult survivors of childhood cancers; however, the standard BSI-18 case-rule has not been validated for this population, and an alternative case rule should be considered.