As a result of a lack of acceptation and self-realization in problem families and school environment young people accede to informal peer group. In some cases it may be criminal peer groups. Then young people as a result the processes of identification and the internalisation may occur accede criminal behaviour. The impact of the peer group on the behavior of members follows through exert strong behavioral pressure, rationalisation of the behaviour of a criminal nature and teaching the techniques of crime. The heard among the members is gained through the recognition of the authority of the significant member of the group who is an impressive to the other by their criminal deeds, and also as a result of the use of acts of violence or threat of its application, boycott among the other member of a group. As we can see very important is the role of a leader who affects the nature, type of criminal behaviour and competition with other unions, the criminal division of tasks between the members of the group and can maintain proper discipline. According to police statistics dominating crimes made by minors are crimes against property, in particular: theft, characters aggravated burglary and armed robbery. The impact of criminal peer group has been manifested through, inter alia: incitement to commit a criminal offence, (which may be also through the use of the authority), mental or physical aiding.