Primary care providers are uniquely able to have an impact on the lives of their patients. Patients generally respect their physicians and will follow advice given about preventive care. The well-informed physician can guide patients about commonly needed vaccines as well as vaccines with fewer indications, such as those for Haemophilus influenzae type B or Lyme disease. Some patients express concerns and reasons to avoid immunization; however, contraindications to vaccination are few and specific. A history of severe immediate-type hypersensitivity reaction to a vaccine or its components (e.g., neomycin, gelatin, egg, baker's yeast) and concurrent moderate-to-severe illness form the basis for most contraindications. A personal history of allergies, penicillin allergy, or a family history of vaccine reaction do not constitute reasons not to vaccinate patients. A history of mild local reaction at the injection site, mild concurrent illness with or without fever, current antibiotic use, or the convalescent phase of an infection also are not valid contraindications. Occasionally, there is concern about the number of vaccines given simultaneously. There is no documented risk of decreased efficacy or increased adverse events with simultaneous administration of numerous vaccines. Any of the vaccines discussed in this article can be administered simultaneously. There is a theoretical concern that an attenuated live virus vaccine might impair the response to a live virus vaccine given subsequently. One should either give these vaccines simultaneously or wait 30 days to give the second one. The administration of immune globulin via packed red blood cells, whole blood, intramuscular immune globulin, or intravenous immune globulin may interfere with viral replication in attenuated vaccinations. After an immune globulin preparation is received, live vaccine should not be administered before the recommended interval, at least 3 months. One should not delay measles-mumps-rubella (MMR) vaccinations in a rubella- or measles-susceptible woman because the patient required anti-RHO immunoglobulin or any other blood product during pregnancy or delivery. If necessary, these patients can be vaccinated after delivery and subsequently tested in 3 months to ensure immunity to rubella or measles. Immune globulin preparations do not interfere with the efficacy of killed vaccines. Breastfeeding is not affected by either killed or live vaccines. No vaccination is contraindicated by breastfeeding. Health care providers in the United States must give a vaccine information statement (VIS) to all vaccine recipients at each dose of diphtheria, tetanus, pertussis, measles, mumps, rubella, polio (either oral or inactivated), hepatitis B, H. influenzae type B, and varicella vaccine as required by the National Childhood Vaccine Injury Act (NCVIA) of 1986. The Centers for Disease Control (CDC) have prepared VISs for other vaccines as well, including pneumococcal polysaccharide, hepatitis A, influenza, and Lyme disease. VISs covered under the NCVIA must not be amended, although the health care worker can add his or her practice name and address. Copies are available from local health departments or on the Web at www.cdc.gov/nip/publications/vis. These documents may be photocopied without prior permission. 1,4 Although current vaccines are safe and efficacious, adverse events have been reported following all vaccines. Selected events must be reported to the Vaccine Adverse Events Reporting System (VAERS). Any adverse event should be reported via this mechanism regardless of whether it is thought to be causally related to the vaccination. VAERS forms are available in the Physician's Desk Reference or by calling a 24-hour recording at 1-800-822-7967.