Answer questions and earn CME/CNE A measles outbreak originating in California during 2014 and 2015 called attention to the potential for infectious disease outbreaks related to underimmunized populations in the United States and the potential risk to pediatric patients with cancer attending school when such outbreaks occur. Compliance with vaccine recommendations is important for the prevention of hepatitis B-related and human papillomavirus-related cancers and for protecting immunocompromised patients with cancer, and these points are often overlooked, resulting in the continued occurrence of vaccine-preventable neoplastic and infectious diseases and complications. This article provides an overview of the importance of vaccines in the context of cancer and encourages clinician, health system, and public policy efforts to promote adherence to immunization recommendations in the United States. CA Cancer J Clin 2017;67:398-410. © 2017 American Cancer Society.