Vaccinations rank among the most effective preventive measures for protection against infectious diseases. Advances in development, production, and control of vaccines facilitate the increasing standards of vaccine safety and tolerance. Comprehensive pre-clinical and clinical tests as well as modern manufacturing and testing methods ensure that vaccines marketed nowadays are safe. As a rule, clinical trials performed before granting the marketing authorisation identify the most frequent adverse events and these results are used to evaluate the safety of the product. Such trials can identify relatively rare adverse events, which occur with a frequency of 1:1,000 to 1:10,000 of all vaccinated individuals. These adverse events will then be included in the summary of product characteristics (SPC) for the vaccine. Even after comprehensive clinical trials of vaccines, it is possible that very rare adverse events may be observed for the first time during general use of a vaccine. In recent years concern over real and alleged risks of vaccines relative to their benefit has grown in many countries including Germany. One reason for this is the fact that most infections that were previously feared have now faded from memory. This situation can be ascribed in part to the success of vaccination. In recent years an increased awareness of substantiated and assumed risks following immunization has been reported in Germany as well as many other countries. In part this may be due to the absence of infectious disease-related mortality and morbidity and to the fact that the severity of vaccine-preventable diseases is no longer observable. Consequently, rare and hypothetical adverse events attain undue public attention. As vaccination willingness diminishes, a resulting lower vaccination rate renders the population susceptible to the natural wild type infection with concomitant increases in mortality and morbidity of vaccine-preventable diseases. Thus, very rare or even unproven adverse events have attracted public attention. Declining vaccination rates resulting from these fears may result in a renewed increase of vaccine-preventable diseases. Adverse events following immunization (AEFI) need to be recognized and adequately assessed. This review presents the scientific knowledge concerning causality and frequency of several AEFI and hypothetical risks.