The nature and importance of the relationship between sex chromosome abnormalities (SCAs) and sexual maladaptive behaviour is uncertain. When considering the aetiology of sexual offending behaviour, the importance of sex chromosome disorder lies in its biopsychological manifestations and in its complex interactions with external influences. At the Adolescent Forensic Service, in keeping with previous research in institutional settings, we found a higher pick‐up rate of SCAs among sexual offenders (5/121) than would be expected in an unbiased community sample (1.2/1000 male livebirths;Jacobs et al. (1992). We present descriptive data on five patients with SCAs out of a total of 121 sexual offenders who presented to the Adolescent Forensic Service over a 6‐year period. We discuss the biopsychosocial features of these five patients and compare them with the remainder of the sexual offenders in the series. We discuss the advantages of early diagnosis and the need for professional vigilance by adolescent forensic psychiatrists, child and adolescent psychiatrists, paediatricians and clinical geneticists.