A growing body of literature has begun to underscore the importance of integrating family-based comprehensive psychological screening into standard medical care for children with oncology and hematology conditions. There are no known family-based measures designed to screen for clinically significant emotional and behavioral concerns in pediatric oncology and hematology patients. The aim of this study was to develop and evaluate the Family Symptom Inventory (FSI), a brief screener of patient and family member psychological symptoms. The FSI also screens for common comorbid physical symptoms (pain and sleep disturbance) and is designed for use at any point during treatment and follow-up. A total of 488 caregivers completed the FSI during regular hematology/oncology visits for 193 cancer, 219 sickle cell disease, and 76 hematology pediatric patients. Exploratory factor analysis, confirmatory factor analysis, and tests of reliability and preliminary validity were conducted. Exploratory factor analysis suggested a 34-item, 4-factor solution, which was confirmed in an independent sample using confirmatory factor analysis (factor loadings=0.49 to 0.88). The FSI demonstrated good internal reliability (α's=0.86 to 0.92) and good preliminary validity. Regular psychosocial screening throughout the course of treatment and follow-up may lead to improved quality of care for children with oncology and hematology conditions.