BACKGROUND In Poland, since 1955 BCG mass vaccinations have been compulsory. During the last two decades the vaccination program has been developed and includes: 1) primary vaccination of the newborn, 2) vaccination of children aged 7 and 12, and 3) revaccination of 18 year old adolescents. More than 95% of newborns and about 80% of older children of this population have been vaccinated. BCG vaccine being in use in Poland bases on the Brazilian/Moreau sub strain and has been producing by the Polish Laboratory. Since 1994 the central register of adverse events of BCG has been introduced by National Tuberculosis and Lung Diseases Institute (NTLDRI). OBJECTIVE The aim of this study was to evaluate the frequency, trends and clinical type of adverse events after BCG vaccination. In addition, correctness of case-finding and treatment of BCG complications was evaluated. METHODS From January 1, 1994 to December 31, 2000 individual data on adverse events, on special card was reported to NTLDRI. Categories of BCG complications was based on classifications proposed by A. Lotte. RESULTS Data of 7,354,780 BCG vaccinated persons was analyzed. Of them 1,559 cases reported AEFI. From the further analysis 98 cases with insufficient data were excluded. The frequency of these cases has been estimated to be 0.2@1000 (2 per 100,000 vaccinated) and was stabile. Among AEFI cases, 773 reported local complication (ulcer, abscess, K.F.) and 647 (44.3%) lymphadenitis including 353 cases with enlargement of lymph nodes and 287 cases of suppurative lymphadenitis (4 per 100,000 vaccinated). Majority of AEFI cases were infants (76%). Only 1 case (infant) with disseminated BCG disease, probably due to the partial interferon gamma receptor deficiency, was reported. Main errors in the diagnosis of complications and the management of adverse events after BCG vaccination were lack of data on the diameter of local changes and size of lymph nodes, as well as attempts to remove the lymph nodes. CONCLUSIONS The results of the study indicate that BCG vaccinations in Poland rarely produce adverse reactions and therefore may be considered as safe method of tuberculosis prevention. Adverse reactions to BCG appears to be underreported. Surveillance of adverse reactions to vaccines should be included in the national immunization program.