Thirteen years ago, while conducting criminological research of juvenile delinquents within a research programme of the Ministry of Education “Juvenile delinquents in the past and today” I decided to research two groups of juvenile delinquents representative for Poland: 1. The first was juvenile delinquents tried in the courts between 1985 and 1988, the choice of files was made on the basis on their availability. According to assumptions I planned to research a representative group of cases of criminal deeds committed by juve-niles and tried in criminal courts in 1980. It appeared to be impossible, files of juveniles from 1980 in 2000 when I organized research were, according to regulations, destroyed (hereinafter I use the term “80’s group”). 2. The second is a sample of a group of cases of criminal deeds committed by ju-veniles and tried in criminal courts in 2000 representative for Poland The main research assumption of the project of research of juvenile delinquents was to investigate and characterize juvenile crime and their social profiles. The research concerned contemporary juveniles – “2000 group” and juveniles in the past who were tried in courts be-tween 1985 and 1989. I intended to investigate juvenile delinquents who belonged to the gen-eration of the parents of those from “2000 group”. Yet a step backward by a generation was impossible (the files were destroyed). I decided that the object of the research will be the group of juvenile delinquents tried in juvenile courts in the 1980s. In 2010 I searched the National Criminal Registry for the records of both “1980s” and “2000 group”. Follow-up period for the latter group was 9 years. After they turned 17 (which is the age limit of legal responsibility under Polish law), from the “2000 group” tried in 2000 in juvenile courts 390 persons, that is 51,3%, were later convicted for crimes. This group, at the moment of record search, was between 20 and 28 and majority of perpetrators were be-tween 24 and 28 – that is young adults in the period of the highest criminal activity. The group of juvenile delinquents from 1980s was 555 persons. The follow-up period was 22 to 22 years. In this group, according to National Criminal Registry information, 187 persons, that is 33,7% had a criminal record at the moment of file search, and they were be-tween 35 and 44. As far as this group is concerned, part of criminal records were erased so a part of convictions in this group remains unknown. Study of previous juvenile delinquents life histories, longitudinal study, criminal career study – these are the names of the same types of research in criminology whose main and common questions is: how many of previous juvenile delinquents commit crimes in adult life. More detailed questions are: - what is the type and significance of crime commited by previus juvenile dalinquents in their adult lives?, - what part of prevous juveline delinquent will become persistent criminals and will commit crimes throughout their adult life until they grow old?, - is it possibile to define etiological factors (risk factors) of persistent offenders which have roots in their situation as minors?, - whom will the justice system meet?; what part of previous juvenile delinquents will become clients of the justice system? In both researched groups previous juvenile delinquents as adults are perpetrators of various types of crimes of which crimes against property and assaults with battery are a sig-nificant proportion. In the younger group – the “2000 group” – one should notice the appear-ance of drug-related crimes and computer crimes. Both groups have a common feature, during a follow-up period one third of previous juvenile delinquents were later convicted only once. Two thirds – more than once. In both groups we also found those who commited more than 10 crimes, these are persistent offenders with a criminal career. Those who will become later persistent offenders and will be convicted many a time during their adult life are – as it can be estimated – approximately 10% of those who are tried in juvenile courts today. This piece of information on the estimated group of persistent offenders is an indication for people in charge of the justice system, punishment execution agendas, and social welfare institutions – concerning what will be the size and cost of the group they will need to take care of. We established the risk factors of becoming an adult offender by examining social profiles of previous juvenile delinquents and by comparing occurrence of certain features in the groups of those who were and were not convicted in adult lives. Juvenile delinquents who were tried for crimes in their adult lives were characterized, in both researched groups, by certain common social features which were much less common in the group of those who did not commit crimes in adult lives: - they had several trial in juvenile courts, - all of them had problems as confirmed by their schools, including behavioural ones (hyperactivity, aggression, vulgar language), - they came from problem families where father had at least a history of alcohol abuse. These findings point to one thing: there is a need and it is useful to intervene in case of such children who have educational and behavioural problems at school early. There is a chance to improve lives of juveniles so that they do not become criminals in adult life. But still, this is only a chance. The justice system will never eliminate persistent offenders, who are also referred to as “career criminals” . Matt DeLisi asks a question: is it ethical to predict behavior of individuals and judge that if a person has a criminal record they will have another one? Is it ethical to use the term “career criminals”? These questions concern also the sense of further research of juvenile de-linquents’ adult lives. Such research are sensible for making a stance how to shape the means of response towards juveniles: the results of research shows that these means should be assis-tance, education and they should include a child and his or her family.