Neuroblastoma is the most common cancer in infants worldwide, but little is known about its etiology. Infectious etiologies involving the immune system have been hypothesized for some childhood cancers, especially leukemia, but the role of infectious agents in neuroblastoma has not been fully investigated. The authors used data from a large case-control study conducted by the Children's Oncology Group in the United States and Canada in 1992-1994 to investigate whether there was any relation among day-care attendance, childhood infections, allergies, and neuroblastoma. They interviewed mothers of 538 case children and 504 age-matched control children by telephone about several factors, including pregnancy, medical history, lifestyle, and childhood medical conditions and exposures. The results suggested decreased risks associated with day-care attendance (odds ratio (OR) = 0.81, 95% confidence interval (CI): 0.56, 1.17), childhood infectious diseases (chickenpox, mumps, red measles, and German measles) (OR = 0.60, 95% CI: 0.39, 0.93), and allergies (OR = 0.68, 95% CI: 0.44, 1.07). The authors found reduced neuroblastoma risk associated with markers of potential childhood infections. This suggests a possible role of infectious agents in neuroblastoma etiology. Future epidemiologic studies should incorporate more direct data on infection.