Neuroblastoma is the most common malignancy in infants and 40% of neuroblastomas are diagnosed in the first year of life. While generally neuroblastoma behaves less aggressively in this age group, tumors that have adverse biologic characteristics do not differ in their behavior from counterparts in older children. Clinical and biologic behavior of neuroblastoma in children up to 460 days of age is similar to that in children less than 1 year of age. Thus the categorization of children up to 18 months of age into risk category is critically dependent on biologic characterization and assignment to appropriate treatment intensity categories. © 2007 Wiley-Liss, Inc.