Consumers perceive probiotics as natural food ingredients, the use of which brings health benefits. There are numerous research studies conducted in a healthy people population and they indicate a good tolerability of probiotics. Adverse events occur rarely, they often are mild and do not require additional interventions. The possibility of serious adverse events should be considered in the case of groups with an increased risk of adverse reactions. In the group of the most seriously ill, probiotics can bring the greatest benefits, but the decision to use them should take into account the potential risk of complications. Despite numerous research studies and meta- analyses, it was not possible to define precise indications and contraindications on the use of probiotics. The  current rules and regulations on the use of probiotics are not uniform. In North America, of key importance is a  principle of long-time and safe for health use of microorganism, which is called a GRAS status (Generally  Recognized as Safe). In the European Union, European Food Safety Authority (EFSA) is responsible for regulation  and monitoring of the safety of probiotics. There is a list of microorganisms that have been considered  safe and are approved for use (QPS – Qualified Presumption of Safety). In North America as well as in Europe the  regulations are restrictive and the claims for approval for use of the new microorganism require numerous and  expensive scientific research. In the paper the safety-in-use of probiotics was assessed in a group of healthy people  and of those with increased risk of adverse reactions. Also the documents were reviewed that regulate the  safe use of microorganisms.