Pediatric oncology patients treated with antineoplastic therapy have impaired immune systems that lead to loss of protective antibodies. They require reimmunization to protect against vaccine-preventable diseases. There are a paucity of studies on the clinical practice of pediatric oncologists and the available recommendations are heterogenous. This study describes current reimmunization practices among pediatric oncologists. We surveyed the Children’s Oncology Group (COG)-identified principle investigators to capture clinical practices among pediatric oncologists within their institutions regarding reimmunization of non–hematopoietic stem cell transplantation patients. The majority of respondents did not routinely assess vaccine-related immune status; those who did most frequently assessed 6 months after cessation of therapies. Methods of assessment included type of therapy received, vaccine titers, and absolute lymphocyte counts. Providers from smaller institutions were more likely to check vaccine titers than those from larger institutions. More than half of the surveyed institutions did not have standardized guidelines available for practitioners. There are variations in reimmunization practices among pediatric oncologists despite available guidelines on recommended schedules. Further research is needed to identify the safest and most cost-effective way to insure immunity to infectious disease after the treatment of childhood cancer.