The article discusses a topical issue in contemporary Bulgaria: the crime among the underage offenders aged 14–17. National Statistical Institute data for a 17 year period is reconfigured, analyzed and then interpreted from the standpoints of sociology of delinquency and criminology. As a result aquantitative generalized profile of the juvenile offender is constructed and presented both in short and in detail.The article also traces the structure and dynamics of the convicted underage offenders throughout the period. Using the correlation method of statistical analysis, the author offers a periodization of the transitional period. The periodization emerges on the basis of changing dynamics explained by the finding that the convicted criminal activity of underage and full age offenders is determined by different factors during the sub-periods. A number of hypothetical explanations, pending verification, are offered in relation to the changes in convicted criminal activity in Bulgaria. The periodization is exclusively based on data and statistical coefficients provided and estimated by the National Statistical Institute.Furthermore, the article discusses the structure and dynamics of convicted underage offenders by a number of demographic and social attributes, e.g. sex, age, education, ethnicity, type of crime, family type, situation in the family, physical and mental health, and all types of inflicted punishments. As a result of all analyses and interpretations based on the available data it is generalized that there are approximately 190 underage (aged 14–17) offenders per year whom can be referred to as dangerous offenders active in Bulgaria.