The main aims of this study were to investigate inter-relationships among offending by three generations of relatives (fathers, mothers, sons, daughters, uncles, aunts, grandfathers and grandmothers) and the concentration of offending in families. This study also investigates how far criminal relatives predict a boy's delinquency. The parents of 1395 Pittsburgh boys aged 8, 11 or 14 reported arrests by all relatives. Parent reports of boys' arrests predicted their later referrals to juvenile court, demonstrating predictive validity. Offenders were highly concentrated in families; if one relative had been arrested, there was a high likelihood that another relative had also been arrested. Arrests of relatives were compared with arrests of the boy, court petitions of the boy, and the boy's reported delinquency (according to the parent, boy and teacher). Arrests of brothers, sisters, fathers, mothers, uncles, aunts, grandfathers and grandmothers all predicted the boy's delinquency. The most important relative was the father; arrests of the father predicted the boy's delinquency independently of all other arrested relatives. Studies of explanatory variables suggested that having a young mother, living in a bad neighbourhood, and low guilt of the boy may be links in the causal chain between arrested fathers and delinquent boys. © 2001 The Association for Professionals in Services for Adolescents.