This study describes epidemiologic findings of pediatric cancer diagnosed in the emergency department (ED) setting. Medical records are retrospectively reviewed on all patients in the hospital's cancer database between 2000 and 2004 who were diagnosed as having cancer or whose oncologic diagnosis was missed during their ED presentation. Of 427 patients identified in the cancer database, 18% (77 of 427) are analyzed. Oncologic diagnosis was missed in 5% (4 of 77) of the eligible patients initially presenting to the ED. The incidence of cancer in the ED is 22.8 cases per 100,000 ED visits. The most prevalent cancer is related to the hematologic system (37.7%), followed by the central nervous system (31.2%) and the abdomen (22.1%). Hematologic, central nervous system, and abdominal cancers constitute approximately 90% of all childhood cancers. Cancer is diagnosed frequently in our ED patient population. Based on the prevalence of certain tumors, the diagnostic approach to children with hematologic, neurologic, or abdominal complaints should include evaluation for any underlying cancer.