Bacillus Calmette-Guérin (BCG) is one of the safest vaccines applied worldwide today. Risk of occurrence of adverse effects upon BCG immunization varies with age of children being vaccinated, whereas local reactivity differs among vaccines due to applied strain as well as the number of viable bacilli and type of vaccine. In 1984, Lotte and co-workers analyzed and classified complications associated with BCG vaccination in detail. This classification is based on clinical, bacteriological, histological and biological information. Category 1 involves extensive local lesions and regional suppuration, BCG-related lymphadenitis, which is usually but not always bacteriologically and/or hitologically confirmed. Categories 2 and 3 comprise more serious complications. Non-fatal cases (localized or multiple changes) are included in category 2, while fatal cases (generalized lesions usually associated with immunodeficiency) are in category 3. Category 4 includes complications which occur upon BCG administration, but not definitely confirmed either bacteriologically or histologically. Keloid formation belongs to this category. Bacillus Calmette-Guerin lymphadenitis is the most common complication of BCG vaccination. There are two forms of BCG adenitis in natural course of lymphadenitis. Simple or non-suppurative lymphadenitis, which usually resolves spontaneously within a few weeks, and suppurative lymphadenitis characterized by fluctuation development with edema and erythema above glands. More serious adverse effects rarely occur at 1-3/1 mil of administered doses. In our country, not all adverse effects related to BCG vaccination have been established However, each complication should be reported, because its monitoring enables quality control both of the vaccine and techniques of its application.