Adverse Events Following Immunization (AEFI) are disadvantageous side effects of preventive vaccination. In 1993 we found 17 cases of AEFI out of 1440 children between 0 and 2 years of age who had received BCG, diphtheria-tetanus-pertussis, measles or poliomyelitis vaccine. They were classified as reactions in 14 children (0.9%) or complications in 3 children (0.2%). Twelve adverse reactions followed DTP vaccination (0.8%), two followed BCG vaccination (0.14%), another two measles vaccination (0.14%) and one followed poliomyelitis vaccination (0.07%). Both generalized and local symptoms were present and they regressed with no further complications. Two children who had received BCG were noted to have a deeply placed abscess at the injection site remaining scar as well as axillary, submandibular and cervical lymph nodes enlargement within 6 months. In a 3 months old child, after the first injection of DTP vaccine, convulsions and consciousness disorder occurred. Transfontanel ultrasonography revealed intraventricular haemorrhage. After one year of intensive neurological care child's health state was improved. In spite of using still more and more safe vaccines none of them is the ideal one--the one with no adverse events following vaccination. Vaccination technics, distribution and storage of vaccines are to be improved which may result in decrease number of AEFI.