This study aims to investigate the predictive validity of externalizing psychopathology for persistence in delinquent behavior when controlling for socio-demographic and first arrest characteristics in childhood first-time arrestees. A sample of first-time arrestees aged under 12 (n = 192) was assessed using the Diagnostic Interview Schedule for Children (DISC-IV) parent-version on attention deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD) and conduct disorder (CD). Based on child and parent reports of offending as obtained at arrest and at 2-year follow-up, three groups of offenders were differentiated: (1) persistent high (n = 48), (2) occasional (n = 62), and (3) persistent low offenders (n = 82). Over one-third of the sample (33.9%) was diagnosed with an externalizing disorder, and 13.5% with both ADHD and ODD or CD. Higher levels of externalizing psychopathology distinguished persistent high offenders from occasional (comorbid ADHD and ODD/CD: OR 8.2, CI 2.6-25.5) and persistent low offenders (comorbid ADHD and ODD/CD: OR 18.2, CI 4.6-72.3; ADHD: OR 4.1, CI 1.3-13.0), over and above socio-demographic and first offense characteristics. Living with both biological parents distinguished the persistent low offenders from the occasional offenders (OR 2.5, CI 1.2-5.0). Since the prevalence of externalizing disorders was high and predicted re-offending, mental health screening and intervention initiatives, aiming at these conditions, should be investigated for this high-risk sample.