Documentation of the safety of any vaccine is of paramount importance given the nature and scale of vaccination as a public health intervention. Prevenar was first approved for use in 2000, and includes seven pneumococcal serotypes conjugated to CRM(197), a carrier protein that has been used safely in multiple conjugate vaccines for more than 20 years. The safety profile of Prevenar was established prior to licensure in 5 clinical trials involving more than 18,000 infants and children. The largest postmarketing study of the safety of Prevenar given concomitantly with other recommended vaccines was conducted in the United States, and included more than 162,000 subjects. This analysis did not suggest any new safety consideration that would alter the risk-benefit balance of the vaccine, and demonstrated the favorable safety profile of Prevenar. To date, global surveillance of spontaneously reported adverse events to the manufacturer after more than 198 million doses distributed has confirmed these findings. The WHO has recommended the priority inclusion of this vaccine in national childhood immunization programs based on both its documented efficacy and safety. We will discuss the importance of monitoring vaccine safety and the methodologies by which this may be done, using Prevenar as an illustrative example.