BACKGROUND This study evaluates the effectiveness and interpretation of hepatitis B (HBV) screening in an at-risk cohort of children with cancer or blood disorders. PROCEDURE We conducted a retrospective epidemiologic analysis of children who screened positive for HBV (HBsAg, HbcAb) from 1999 to 2009 at a quaternary children's hospital, focusing on patients with hematologic and oncologic conditions. Descriptive statistics were generated for demographics and serologies. Follow-up of positive serologies and clinical outcomes were analyzed. RESULTS A total of 12,754 children were screened for HBV. Of 391 that screened positive, 118 had a hematologic or oncologic diagnosis. Leukemia, anemia, and thrombocytopenia comprised 84% of diagnoses. The majority (98%) tested HBcAb positive but only 20% received confirmatory HBV DNA testing. Three patients (13% of those HBV DNA tested) were identified to have chronic disease. HBV was not a known pre-existing condition, and chemotherapy preceded HBV diagnosis in all cases. CONCLUSIONS The majority of children with cancer or blood disorders who screened HBV positive did not receive follow-up DNA testing, exposing them to reactivation risk and delaying definitive therapy. HBcAb may be the only indicator of chronic HBV infection and DNA confirmation should be routine. Our findings suggest a significant number of additional patients eligible for HBV treatment may have been identified with reflexive DNA testing.