Vaccines have been exceptionally effective against diseases such as smallpox, measles, chickenpox, and polio. They are among the safest and most cost-effective agents for disease prevention. In recent years, vaccination has been considered for other diseases, including AIDS and cancer. Cancer vaccines can be categorized as preventive or therapeutic. Preventive vaccines, which are commercially available for cervical cancer and liver cancer, block infection with the causative agents of human papillomavirus and hepatitis B virus, respectively. The benefit of cancer treatment vaccines lies in their ability to "boost" the immune system response to cancer cells, which is generally low. Using vaccines in the treatment of cancer is relatively new, however, and chiefly experimental. Therapeutic vaccines for breast, lung, colon, skin, renal, prostate, and other cancers are now being investigated in clinical trials. Oncology nurses may play a significant role in reducing barriers to uptake of preventive vaccines among the general public and in increasing patients' acceptance of therapeutic cancer vaccines.